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: If2587dbbbdc88ab01d1fb16ab6b5efe446453957
Story: #2002586
Task: #24315

mikalstill/nova,gooddata/openstack-nova,openstack/nova,rahulunair/nova,klmitch/nova,mahak/nova,mikalstill/nova,mahak/nova,mahak/nova,rahulunair/nova,gooddata/openstack-nova,gooddata/openstack-nova,klmitch/nova,mikalstill/nova,klmitch/nova,klmitch/nova,rahulunair/nova,gooddata/openstack-nova,openstack/nova,openstack/nova