Updated openstack/openstack
Project: openstack/nova  f31652a762a7c3de83431f5a8a1d3cc7eaf8f917

libvirt: speed up get_memory_mb_used method

Switch the get_memory_mb_used method to use the new
list_instance_domains method.

Blueprint: libvirt-domain-listing-speedup
Change-Id: I6f9e9a2ee761b81e8fc06237cfef1b7202effe37