Add config options for enabled extensions

This commit adds a new set of config options to the feature_enabled
groups for a list of enabled extensions. These options are used to
specify whether all extensions are enabled or which subset is expected
to be enabled. This just sets up the initial framework for doing
this and converts the FlavorExtraSpecs tests to use it.

paritally implements bp config-cleanup

Change-Id: I6a5a9b16e62eb8a216334a0662c99f0dd0d16873
Updated from global requirements

Change-Id: Ia54c5fb8815a586a9686adc38f6a88967f7a099d
Merge "Add config options for enabled extensions"
Rename create_test_server to create_temp_server

Change https://review.openstack.org/#/c/58645/ introduced bug 1247161 when
running under nose as the method name includes "test".
Renamed to not use test and updated HACKING to give advice against using
"test" in a method name.

Closes-bug: 1247161

Change-Id: I9f6d7d5fc9b3b94e1fbf395a62177c8df7e9f5b4