Refactor Tower HA Instance logic and models

* Gut the HA middleware
* Purge concept of primary and secondary.
* UUID is not the primary host identifier, now it's based mostly on the
  username.  Some work probably still left to do to make sure this is
  legit.  Also removed unique constraint from the uuid field.  This
  might become the cluster ident now... or it may just deprecate
* No more secondary -> primary redirection
* Initial revision of /api/v1/ping
* Revise and gut tower-manage register_instance
* Rename awx/main/socket.py to awx/main/socket_queue.py to prevent
  conflict with the "socket" module from python base
* Revist/gut the Instance manager... not sure if this manager is really
  needed anymore

awx/main/utils.py

@@ -425,7 +425,7 @@ def get_system_task_capacity():
 
 
 def emit_websocket_notification(endpoint, event, payload, token_key=None):
-    from awx.main.socket import Socket
+    from awx.main.socket_queue import Socket
 
     try:
         with Socket('websocket', 'w', nowait=True, logger=logger) as websocket: