Add python 3.6 unit test job
Add python 3.6 unit test job

This is a mechanically generated patch to add a unit test job running
under Python 3.6 as part of the python3-first goal.

See the python3-first goal document for details:
https://governance.openstack.org/tc/goals/stein/python3-first.html

Change-Id: I82ebe70f3108d4db07b4c8e929fe551541150f90

openstack/python-searchlightclient,openstack/python-searchlightclient