Address review in named_servers

from willingc

- consistency of repr/str when logging usernames
- cleanup some attribute declarations
- add comments about db session weirdness

jupyterhub/user.py

@@ -88,6 +88,7 @@ class User(HasTraits):
     def _log_default(self):
         return app_log
 
+    spawners = None
     settings = Dict()
 
     db = Any(allow_none=True)
@@ -103,7 +104,10 @@ class User(HasTraits):
         # db session changed, re-get orm User
         db = change.new
         if self._user_id is not None:
+            # fetch our orm.User from the new db session
             self.orm_user = db.query(orm.User).filter(orm.User.id == self._user_id).first()
+        # update our spawners' ORM objects with the new session,
+        # which can be found on our new orm_user.
         for name, spawner in self.spawners.items():
             spawner.orm_spawner = self.orm_user.orm_spawners[name]
 
@@ -116,8 +120,6 @@ class User(HasTraits):
         else:
             self._user_id = None
 
-    spawners = None
-
     @property
     def authenticator(self):
         return self.settings.get('authenticator', None)