Remove whitespace from unix group names

(cherry picked from commit d0e3d75381)

lib/ansible/modules/system/user.py

@@ -552,7 +552,7 @@ class User(object):
         if self.groups is None:
             return None
         info = self.user_info()
-        groups = set(filter(None, self.groups.split(',')))
+        groups = set([x.strip() for x in self.groups.split(',') if x])
         for g in set(groups):
             if not self.group_exists(g):
                 self.module.fail_json(msg="Group %s does not exist" % (g))