Convert test_backend_ldap to config fixture

The test_backend_ldap module wasn't using the config fixture for
setting config options.

Change-Id: I3f0e1ba13f0be3625db5a7eb275a3d7fd2bd41e5
Adds style checks to ease reviewer burden

The following checks were added in this commit:

 - mutable default args are no longer allowed
 - block comments must begin with at least one space
 - enforce assertIsNone instead of assertEqual with a None

bp more-code-style-automation

Change-Id: I7dba0c8b45078a665d40993d751c79566aa7505f
Merge "Adds style checks to ease reviewer burden"
Merge "Convert test_backend_ldap to config fixture"