Refactor user_and_group so it works off of numbers

There are various cases where a UID to username to UID mapping breaks
down. One UID can be used by two usernames, or no username. If we
always use UIDs internally, then these ambiguous cases won't be a
problem.

lib/ansible/module_common.py

@@ -319,15 +319,7 @@ class AnsibleModule(object):
         st = os.stat(filename)
         uid = st.st_uid
         gid = st.st_gid
-        try:
-            user = pwd.getpwuid(uid)[0]
-        except KeyError:
-            user = str(uid)
-        try:
-            group = grp.getgrgid(gid)[0]
-        except KeyError:
-            group = str(gid)
-        return (user, group)
+        return (uid, gid)
 
     def set_default_selinux_context(self, path, changed):
         if not HAVE_SELINUX or not self.selinux_enabled():
@@ -366,8 +358,7 @@ class AnsibleModule(object):
         path = os.path.expanduser(path)
         if owner is None:
             return changed
-        user, group = self.user_and_group(path)
-        if owner != user:
+        orig_uid, orig_gid = self.user_and_group(path)
         try:
             uid = int(owner)
         except ValueError:
@@ -377,6 +368,7 @@ class AnsibleModule(object):
                 self.fail_json(path=path, msg='chown failed: failed to look up user %s' % owner)
         if self.check_mode:
             return True
+        if orig_uid != uid:
             try:
                 os.chown(path, uid, -1)
             except OSError:
@@ -388,10 +380,7 @@ class AnsibleModule(object):
         path = os.path.expanduser(path)
         if group is None:
             return changed
-        old_user, old_group = self.user_and_group(path)
-        if old_group != group:
-            if self.check_mode:
-                return True
+        orig_uid, orig_gid = self.user_and_group(path)
         try:
             gid = int(group)
         except ValueError:
@@ -399,6 +388,9 @@ class AnsibleModule(object):
                 gid = grp.getgrnam(group).gr_gid
             except KeyError:
                 self.fail_json(path=path, msg='chgrp failed: failed to look up group %s' % group)
+        if self.check_mode:
+            return True
+        if orig_gid != gid:
             try:
                 os.chown(path, -1, gid)
             except OSError:
@@ -478,7 +470,17 @@ class AnsibleModule(object):
         if path is None:
             return kwargs
         if os.path.exists(path):
-            (user, group) = self.user_and_group(path)
+            (uid, gid) = self.user_and_group(path)
+            kwargs['uid'] = uid
+            kwargs['gid'] = gid
+            try:
+                user = pwd.getpwuid(uid)[0]
+            except KeyError:
+                user = str(uid)
+            try:
+                group = grp.getgrgid(gid)[0]
+            except KeyError:
+                group = str(gid)
             kwargs['owner'] = user
             kwargs['group'] = group
             st = os.stat(path)