Helper methods to support the narrowed localhost exception
Localhost exception fixes for functional tests
Localhost exception fixes for threading tests
Add authentication necessary for replication tests
Rename add_admin_user to ensure_admin_user everywhere
Authentication tests should attempt to use an existing admin user first.
Localhost exception fixes for replica_set tests
clear_admin_user should be resilient to being called twice.
Replace hard-wired 13 with constant AUTH_ERROR
Update sharding tests to handle narrowed localhost exception
Restructure ensure_auth method so it does not affect pre-2.7.1 servers