Set libvirt live_migration_uri

Sets up n-cpu to migrate domains via SSH.  By default, hosts attempt
to connect to each other as root, so this specifies STACK_USER instead.

Change-Id: Ic6e868091c89a2cc6b2f0fada3f7e95002aaff8b
Merge "Set libvirt live_migration_uri"
Merge branch 'master' of https://github.com/openstack-dev/devstack