extract fixtures from nova.test to nova.test.fixtures

Start extracting all the setup code in note.test into fixtures which
will let us decompose test setup (and have test base classes that
don't setup everything).

This creates new OutputStreamCapture fixture and StandardLogging
fixture and unit tests for both of them plus tests for the exiting
Conf fixture.

H305/306 have to be turned off because hacking import rules are broken
and continue to believe that fixtures is a nova module not the
absolute one.

Change-Id: I97fdacdf5a6ad2957b0efa1e21ae084d4eb04ab9
Merge "extract fixtures from nova.test to nova.test.fixtures"