Add tests for SessionClient
Add tests for SessionClient

Change-Id: I22913a7277a8eacfe6bfdb947ff7d6693f527330
Closes-bug: #1427596

ecerulm/python-heatclient,openstack/python-heatclient,ecerulm/python-heatclient,tcpcloud/python-heatclient,tcpcloud/python-heatclient