Prepare for Identity v3 tests

* Split identity/fakes.py for v2_0 and v3
* Split identity/test_identity.py for v2_0 and v3
* Fix issues in commands with enable/disable
* Clean up v2 commands

Change-Id: I6e536b6a130fc556dbd7dcf9f2e76d939ca1bc1c
Identity v3 tests

* Add project, user, role and service v3 tests
* Fix issues in commands with enable/disable
* Make commands and tests more consistent between versions
* Make formatting and comments more consistent

Change-Id: Id21e7a5abd7e421a7742f937861ec46b53095fc7