Fix for #3062 additional groups should only be added once.

Also consolidated duplicate groups code into one get_groups_set() method.
Removed unused call to user_group_membership.
Removed sorting operations on set functions cause sets are inherently unordered.
Minor style improvements to match the rest of the code.

The new function will make the order of group names passed to the system command less determistic.
Which was already the case for modify_user_usermod() but not for other methods.
It will also strip out duplicate group names automatically which was not always the case previously.

library/system/user

@@ -229,7 +229,7 @@ class User(object):
         # select whether we dump additional debug info through syslog
         self.syslogging = False
 
-    def execute_command(self,cmd):
+    def execute_command(self, cmd):
         if self.syslogging:
             syslog.openlog('ansible-%s' % os.path.basename(__file__))
             syslog.syslog(syslog.LOG_NOTICE, 'Command %s' % '|'.join(cmd))
@@ -263,12 +263,9 @@ class User(object):
             cmd.append(self.group)
 
         if self.groups is not None:
-            if self.groups != '':
-                for g in self.groups.split(','):
-                    if not self.group_exists(g):
-                        self.module.fail_json(msg="Group %s does not exist" % (g))
+            groups = self.get_groups_set()
             cmd.append('-G')
-            cmd.append(self.groups)
+            cmd.append(','.join(groups))
 
         if self.comment is not None:
             cmd.append('-c')
@@ -326,12 +323,8 @@ class User(object):
                 if current_groups and not self.append:
                     groups_need_mod = True
             else:
-                groups = self.groups.split(',')
-                for g in groups:
-                    if not self.group_exists(g):
-                        self.module.fail_json(msg="Group %s does not exist" % (g))
-
-                group_diff = set(sorted(current_groups)).symmetric_difference(set(sorted(groups)))
+                groups = self.get_groups_set()
+                group_diff = set(current_groups).symmetric_difference(groups)
 
                 if group_diff:
                     if self.append:
@@ -370,6 +363,7 @@ class User(object):
             return (0, '', '')
 
         cmd.append(self.name)
+        open("/tmp/xxx.log", "a").write(str(cmd)+"\n")
         return self.execute_command(cmd)
 
     def group_exists(self,group):
@@ -391,11 +385,23 @@ class User(object):
         else:
             return list(grp.getgrnam(group))
 
+    def get_groups_set(self):
+        if self.groups is None:
+            return None
+        info = self.user_info()
+        groups = set(self.groups.split(','))
+        for g in set(groups):
+            if not self.group_exists(g):
+                self.module.fail_json(msg="Group %s does not exist" % (g))
+            if info and self.group_info(g)[2] == info[3]:
+                groups.remove(g)
+        return groups
+
     def user_group_membership(self):
         groups = []
         info = self.get_pwd_info()
         for group in grp.getgrall():
-            if self.name in group.gr_mem and info[3] == group.gr_gid:
+            if self.name in group.gr_mem and not info[3] == group.gr_gid:
                 groups.append(group[0])
         return groups
 
@@ -574,11 +580,9 @@ class FreeBsdUser(User):
             cmd.append(self.group)
 
         if self.groups is not None:
-            for g in self.groups.split(','):
-                if not self.group_exists(g):
-                    self.module.fail_json(msg="Group %s does not exist" % (g))
+            groups = self.get_groups_set()
             cmd.append('-G')
-            cmd.append(self.groups)
+            cmd.append(','.join(groups))
 
         if self.createhome:
             cmd.append('-m')
@@ -644,12 +648,9 @@ class FreeBsdUser(User):
 
         if self.groups is not None:
             current_groups = self.user_group_membership()
-            groups = self.groups.split(',')
-            for g in groups:
-                if not self.group_exists(g):
-                    self.module.fail_json(msg="Group %s does not exist" % (g))
+            groups = self.get_groups_set()
 
-            group_diff = set(sorted(current_groups)).symmetric_difference(set(sorted(groups)))
+            group_diff = set(current_groups).symmetric_difference(groups)
             groups_need_mod = False
 
             if group_diff:
@@ -732,11 +733,9 @@ class SunOS(User):
             cmd.append(self.group)
 
         if self.groups is not None:
-            for g in self.groups.split(','):
-                if not self.group_exists(g):
-                    self.module.fail_json(msg="Group %s does not exist" % (g))
+            groups = self.get_groups_set()
             cmd.append('-G')
-            cmd.append(self.groups)
+            cmd.append(','.join(groups))
 
         if self.comment is not None:
             cmd.append('-c')
@@ -799,12 +798,8 @@ class SunOS(User):
 
         if self.groups is not None:
             current_groups = self.user_group_membership()
-            groups = self.groups.split(',')
-            for g in groups:
-                if not self.group_exists(g):
-                    self.module.fail_json(msg="Group %s does not exist" % (g))
-
-            group_diff = set(sorted(current_groups)).symmetric_difference(set(sorted(groups)))
+            groups = self.get_groups_set()
+            group_diff = set(current_groups).symmetric_difference(groups)
             groups_need_mod = False
 
             if group_diff:
@@ -901,11 +896,9 @@ class AIX(User):
             cmd.append(self.group)
 
         if self.groups is not None:
-            for g in self.groups.split(','):
-                if not self.group_exists(g):
-                    self.module.fail_json(msg="Group %s does not exist" % (g))
+            groups = self.get_groups_set()
             cmd.append('-G')
-            cmd.append(self.groups)
+            cmd.append(','.join(groups))
 
         if self.comment is not None:
             cmd.append('-c')
@@ -954,12 +947,8 @@ class AIX(User):
 
         if self.groups is not None:
             current_groups = self.user_group_membership()
-            groups = self.groups.split(',')
-            for g in groups:
-                if not self.group_exists(g):
-                    self.module.fail_json(msg="Group %s does not exist" % (g))
-
-            group_diff = set(sorted(current_groups)).symmetric_difference(set(sorted(groups)))
+            groups = self.get_groups_set()
+            group_diff = set(current_groups).symmetric_difference(groups)
             groups_need_mod = False
 
             if group_diff:
@@ -1113,7 +1102,6 @@ def main():
         result['comment'] = info[4]
         result['home'] = info[5]
         result['shell'] = info[6]
-        groups = user.user_group_membership()
         result['uid'] = info[2]
         if user.groups is not None:
             result['groups'] = user.groups