[virsh] Ensure volume pool has a default value
[virsh] Ensure volume pool has a default value

When importing an image set, the host may not have a volume
pool setup yet and will therefore have no value for the pool
path. We provide a suitable default if it is missing.

Change-Id: Ie97c67ff918e284956192e4735cd41528094599c

redhat-openstack/infrared,redhat-openstack/infrared,redhat-openstack/infrared