Adds support for Keystone V3 API

Updated trove client to support Keystone V3 API. The
Keystoneclient session object is used for authentication, retrieving
the service catalog and HTTP connection/session management.

Added additional CLI parameters for Keystone V3.

Added tests using requests_mock instead of mocking completely the
session object like the previous failed patch:

https://review.openstack.org/#/c/102315

Change-Id: Ib804c0a45b3b4d3f8670ec642b2c2fd1be6cd656
Merge "Adds support for Keystone V3 API"