[evil] Remove OpenStack related plugins

NOTE: the existing legacy jobs should continue working due to several
applied hacks.

The new home for OpenStack plugins:
  https://git.openstack.org/cgit/openstack/rally-openstack
  https://github.com/openstack/rally-openstack
  https://pypi.org/project/rally-openstack/

Change-Id: I36e56759f02fe9560b454b7a396e0493da0be0ab