add domain, credential to identity v3 api

moved policy.py to it's own patch
minor changes based on comments
reworked it now that the domain specs have changed
added credential - create, delete, update, show, list
added domain - create, delete, update, show, list
update setup.py entry points

Change-Id: I6bbbb8fdfbc3e76ba75374e9579eb92c96c928fe
Merge "add domain, credential to identity v3 api"