Don't traceback if a gid is specified instead of a group name

Fixes https://github.com/ansible/ansible/issues/9796

lib/ansible/modules/system/user.py

@@ -447,11 +447,12 @@ class User(object):
 
     def group_exists(self,group):
         try:
-            if group.isdigit():
+            # Try group as a gid first
-                if grp.getgrgid(int(group)):
+            grp.getgrgid(int(group))
             return True
-            else:
+        except (ValueError, KeyError):
-                if grp.getgrnam(group):
+            try:
+                grp.getgrnam(group)
                 return True
             except KeyError:
                 return False
@@ -459,9 +460,10 @@ class User(object):
     def group_info(self, group):
         if not self.group_exists(group):
             return False
-        if group.isdigit():
+        try:
-            return list(grp.getgrgid(group))
+            # Try group as a gid first
-        else:
+            return list(grp.getgrgid(int(group)))
+        except (ValueError, KeyError):
             return list(grp.getgrnam(group))
 
     def get_groups_set(self, remove_existing=True):