Use tempest.lib tenants_client

Tempest 12.1.0 has been released for new library interfaces.
These interfaces are stable[1] and we need to switch using them
instead of current using unstable interfaces.
This will be helpful to avoid breaking gate jobs.

[1]: https://github.com/openstack/tempest/blob/master/doc/source/library.rst#stability

Change-Id: I74a5d5ed43f758b88a22ded293d85d046005d41f
1 file changed
tree: cdc0171073f363480929ce8ea9b9e5e093e113e1
  1. neutron/