Add a config option for trusts

This commit adds a new config section identity-feature-enabled which
contains the options to select which optional/configurable features in
keystone are enabled. The only option that fits this category at this
time is trusts.

Partially implements bp config-cleanup

Change-Id: I8110156e48616534c45e9eb2c12557b2d6bdfd46
Make BaseV2MemeberImageTest inherits from BaseV2ImageTest

Without this patch BaseV2MemeberImageTest inherits from BaseImageTest
which permits all tests using BaseV2MemeberImageTest to run even if
glance API v2 is not supported

Change-Id: Ibe350204098aa1a37db1ed45269d6b087a8dde4a
Closes-Bug: #1269815
Merge "Make BaseV2MemeberImageTest inherits from BaseV2ImageTest"
Merge "Add a config option for trusts"