A complete rewrite of this LWRP

The previous LWRP used HTTP to interrogate and modify
opentstack-identity data. As the API is somewhat of a moving target,
migrate the register provider to include everything it had previously,
combine that with the credentials provider, and rework all the
identity calls to use the identity (keystone) CLI tools.

Change-Id: I4230f047ee9c26d076ad14c48afac73f0e92c4ad