Fix tox for running py3.6
Fix tox for running py3.6

Fix unit tests to run with py3.6.

Change-Id: I96d8e28fe22d5344576caf49f6f7631b96e87b0f
Signed-off-by: Chuck Short <61c7e57c8f71fbf1f6c3fcd85c16ccd0f494e116@redhat.com>

openstack/refstack-client,openstack/refstack-client,stackforge/refstack-client,stackforge/refstack-client