upgrade testing as part of the gate

Registered by Sean Dague

Dean Troyer's grenade effort needs to get into
the nightly testing on the ci team, and the results should be coming out
to the qa team.


Fixes and tests on grenade are still on going. Next steps are running tempest smoke tests after upgrade is complete and successfully running


Work Items

Work items:
* Add smoke tests to grenade (https://review.openstack.org/32460): DONE
* Change from quantum to neutron on upgrading (https://review.openstack.org/#/c/36112): DONE
* Enable services for gate-grenade-devstack-vm (https://review.openstack.org/34262): DONE
* Allow target exercises to run independently (https://review.openstack.org/36513) : DONE
* Add devstack-vm-grenade job to grenade (https://review.openstack.org/#/c/36876 ): INPROGRESS

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