hobo_notify: use publisher.user_class (#8664)

Using wcs.users.User directly is incompatible with SQL storage.

wcs/ctl/hobo_notify.py

@@ -154,9 +154,10 @@ class CmdHoboNotify(Command):
 
     @classmethod
     def provision_user(cls, publisher, issuer, action, data, full=False):
-        from wcs.users import User
         from wcs.roles import Role
 
+        User = publisher.user_class
+
         assert not full # full is not supported for users
 
         for o in data: