fill in postgres application_name on connection

* Tried to fill in application_name in awx/__init__.py but I think that
is too late
* Fill in database application_name with enough information to easily
trace the connection from postgres back to the node and pid that
initiated the connection.
* Set application_name in django settings so that application_name is
set _before_ the first postgres connection is established.

awx/main/management/commands/check_migrations.py

@@ -8,5 +8,7 @@ class Command(MakeMigrations):
     def execute(self, *args, **options):
         settings = connections['default'].settings_dict.copy()
         settings['ENGINE'] = 'sqlite3'
+        if 'application_name' in settings['OPTIONS']:
+            del settings['OPTIONS']['application_name']
         connections['default'] = DatabaseWrapper(settings)
         return MakeMigrations().execute(*args, **options)