Specify LIBVIRT_DEFAULT_URI for nova-compute os-svc-install

This allows baremetal calls from seed to host to work when the host
does not have qemu:///system as the default libvirt uri.
Closes-Bug: #1226310

Change-Id: I1279bb1b303c81a7ae627ee0b579302e5163d398
Merge "Specify LIBVIRT_DEFAULT_URI for nova-compute os-svc-install"