refactor(endpoints/api/superuser*): refactored code behind db model

this moves all the db model code behind an interface in prep for v2-2

Issue: https://coreosdev.atlassian.net/browse/QUAY-750

- [ ] It works!
- [ ] Comments provide sufficient explanations for the next contributor
- [ ] Tests cover changes and corner cases
- [ ] Follows Quay syntax patterns and format

data/model/user.py

@@ -217,6 +217,11 @@ def update_email(user, new_email, auto_verify=False):
     raise DataModelException('E-mail address already used')
 
 
+def update_enabled(user, set_enabled):
+  user.enabled = set_enabled
+  user.save()
+
+
 def create_robot(robot_shortname, parent):
   (username_valid, username_issue) = validate_username(robot_shortname)
   if not username_valid: