Improve default logging configuration

By default, a number of serious exceptions were not being
logged. Adding a logger for 'django'-related logs resolves this.

Also:
 - Add loggers for missing clients and django_openstack_auth
 - Add a default level for individual loggers (what makes it out to
   the log file remains determined by the handler configuration)

Change-Id: Id3478ac8ec79f22c19ef66e747f3701f98a36611
Closes-Bug: #1236423
Merge "Improve default logging configuration"