requeue websocket messages that don't (yet) have an established user

There's a race between our `ws_connect` and `ws_receive` methods;
it's possible to fall into a scenario where we're handling a legitimate
message *before* django-channels is able to persist the `user_id` into
the channel session.  This results in a scenario where a user can open
a browser tab and never receive new websocket messages.  In this
scenario, we should just toss the message back into the queue and try
again later (up to a reasonable limit of retries).

awx/settings/defaults.py

@@ -866,6 +866,11 @@ TOWER_SETTINGS_MANIFEST = {}
 
 LOG_AGGREGATOR_ENABLED = False
 
+# The number of retry attempts for websocket session establishment
+# If you're encountering issues establishing websockets in clustered Tower,
+# raising this value can help
+CHANNEL_LAYER_RECEIVE_MAX_RETRY = 10
+
 # Logging configuration.
 LOGGING = {
     'version': 1,