Libvirt shuts down existing virtual machines. To solve this problem,
the /var/lib/libvirt directory needs to be persisted. By persisting
this directory in the nova data container, libvirt can communicate
with the sockets setup by the previous data container.
Change-Id: I362c533f8493984123686fe6e3f8e43d97434ca6
Closes-Bug: #1494060