Prepare context tests for new to_dict() attributes
Prepare context tests for new to_dict() attributes

The pending release of oslo.context (2.6.0) introduces a new attribute
to the to_dict() method that will break tests that do a exact dictionary
comparison.  This patch creates a smarter forward compatible approach
to enable existing tests to function as designed and support new
attributes without failure.

Change-Id: Icd7a320a418c339f02f2f6283187a7ce3f7a8135
Closes-Bug: #1603193
stackforge/senlin,openstack/senlin,openstack/senlin,stackforge/senlin,openstack/senlin