Do not accept enterprise licenses in some cases.

This commit makes it so that enterprise licenses are rejected in HA
environments if there is no active MongoDB server.

Additionally, it suppresses trying to connect to MongoDB in cases where
it is not present or meaningful.

awx/settings/defaults.py

@@ -5,8 +5,6 @@ import os
 import sys
 from datetime import timedelta
 
-MONGO_DB = 'system_tracking'
-
 # Update this module's local settings from the global settings module.
 from django.conf import global_settings
 this_module = sys.modules[__name__]