Rename "admin_tenant_name" to "admin_project_name" and
rename "tenant_name" to "project_name". These configs have been
renamed in tempest [1], so Magnum needs to adapt the change.
In addition, enable the required devstack plugins in gate hook,
since they has been removed from project-config [2].
[1] https://review.openstack.org/#/c/301167/
[2] https://review.openstack.org/#/c/305475/
Change-Id: I41438cbfaefd9d04d7e73a4f46f5ece1494b349c
Closes-Bug: #1567691
(partially pick from commit b8324f0d72)
fff3c0c08c