Add neutron functional job to devstack check queue

The neutron functional job has a 100% success rate since being being
enabled as a non-voting check job for neutron.  Since the job depends
on devstack to deploy dependencies, this change adds the job to
devstack's check queue as a precondition to allowing it to vote/gate.

Implements: blueprint neutron-testing-refactor
Change-Id: I956bda160dc972ee3671c9c9646dc8910cbd583a
Merge "Add neutron functional job to devstack check queue"