Cherry pick Identity API with keystone client from https://review.openstack.org/#/c/38316

Indicate how to use v3 Identity API with keystone client and openstack client.

Fix bug 1194223

Change-Id: I692243bc3e87c6a02937d59d8ee34f874deb9669
Merge "Cherry pick Identity API with keystone client from https://review.openstack.org/#/c/38316" into stable/grizzly