Add Identity v2 project tests

* establish the the form of cliff command classes
* implement some common fake objects
* implement Identity command tests for v2 project
* fix stdout/stderr capture

Also re-work the project create and set commands for exclusive options
(--enable|--disable) to actually behave properly.  Yay tests!

Change-Id: Icbb313db544c1f8dd3c9af7709971838b5a4d115