Update for hypervisor_client API change
Update for hypervisor_client API change

Community patch https://review.openstack.org/#/c/190484/ change
the REST API for the hypervisor_client causing the multi-node
test to fail.  This patch updates the multinode test to use
the new API interface.

Change-Id: I8057ac277175b7836d132fe4faf92f48c2d9a8bb

cisco-openstack/tempest,cisco-openstack/tempest