add python 3.7 unit test job
add python 3.7 unit test job

This is a mechanically generated patch to add a unit test job running
under Python 3.7.

See ML discussion here [1] for context.

[1] http://lists.openstack.org/pipermail/openstack-dev/2018-October/135626.html

Change-Id: Icb3631a9a9a1f0916013a3c4bf375b1b447f755d
Story: #2004073
Task: #27457

openstack/aodh,openstack/aodh