Fixes issue #315

This adds some logic when usings groups possibly in combination with append

  if just specifying groups and the current groups do not match the list
     set groups
  if specifying groups with append and any group thats not in the current groups
     set groups with -a

user

@@ -135,14 +135,28 @@ def user_mod(user, **kwargs):
                 cmd.append('-g')
                 cmd.append(kwargs[key])
         elif key == 'groups' and kwargs[key] is not None:
-            defined_groups = kwargs[key].split(',')
-            for g in defined_groups:
+            current_groups = user_group_membership(user)
+            groups = kwargs[key].split(',')
+            for g in groups:
                 if not group_exists(g):
                     fail_json(msg="Group %s does not exist" % (g))
-            existing_groups = user_group_membership(user)
-            if sorted(defined_groups) != sorted(existing_groups):
+            group_diff = set(sorted(current_groups)).symmetric_difference(set(sorted(groups)))
+            groups_need_mod = False
+
+            if group_diff:
+                if kwargs['append'] is not None and kwargs['append'] == 'yes':
+                    for g in groups:
+                        if g in group_diff:
+                            cmd.append('-a')
+                            groups_need_mod = True
+                else:
+                   debug("groups differ, trigger usemod")
+                   groups_need_mod = True
+
+            if groups_need_mod:
                 cmd.append('-G')
-                cmd.append(kwargs[key])
+                cmd.append(','.join(groups))
+
         elif key == 'comment':
             if kwargs[key] is not None and info[4] != kwargs[key]:
                 cmd.append('-c')