Cleanup, Improve coverage of swift::keystone::auth spec tests

Refactor with shared examples, improves coverage with 12 additional
tests.

Change-Id: Ie686af051f11941a88ea479b1d9187560f8140bb
Fix include_class deprecation warning. Use contain_class instead.

Change-Id: I9ab9e1d72a06b2de0d63601795b0902e53f330b6
Merge "Cleanup, Improve coverage of swift::keystone::auth spec tests"