Respect storage pool path in create-nodes script

The create-nodes script didn't cope well with libvirt storage pool
named "default" being in non-standard location. It created the images
in correct location, but passed incorrect image path into configure-vm
script, because the image path was hard coded.

Now the script queries for correct location of the image using virsh.

Change-Id: Ia049a7496d4df0ae9f0c606a3d6279b9f94c56fc
Merge "Respect storage pool path in create-nodes script"