Make host range parsing errors issue better messages

Now we always say "host range must …specific thing…"

lib/ansible/inventory/expand_hosts.py

@@ -79,7 +79,7 @@ def expand_hostname_range(line = None):
         (head, nrange, tail) = line.replace('[','|',1).replace(']','|',1).split('|')
         bounds = nrange.split(":")
         if len(bounds) != 2 and len(bounds) != 3:
-            raise errors.AnsibleError("host range incorrectly specified")
+            raise errors.AnsibleError("host range must be begin:end or begin:end:step")
         beg = bounds[0]
         end = bounds[1]
         if len(bounds) == 2:
@@ -89,11 +89,11 @@ def expand_hostname_range(line = None):
         if not beg:
             beg = "0"
         if not end:
-            raise errors.AnsibleError("host range end value missing")
+            raise errors.AnsibleError("host range must specify end value")
         if beg[0] == '0' and len(beg) > 1:
             rlen = len(beg) # range length formatting hint
             if rlen != len(end):
-                raise errors.AnsibleError("host range format incorrectly specified!")
+                raise errors.AnsibleError("host range must specify equal-length begin and end formats")
             fill = lambda _: str(_).zfill(rlen)  # range sequence
         else:
             fill = str
@@ -102,7 +102,7 @@ def expand_hostname_range(line = None):
             i_beg = string.ascii_letters.index(beg)
             i_end = string.ascii_letters.index(end)
             if i_beg > i_end:
-                raise errors.AnsibleError("host range format incorrectly specified!")
+                raise errors.AnsibleError("host range must have begin <= end")
             seq = [string.ascii_letters[i] for i in range(i_beg, i_end+1, int(step))]
         except ValueError:  # not an alpha range
             seq = range(int(beg), int(end)+1, int(step))