virsh_volume: Adjust for upstream change

Upstream change adjusted the output of the virsh vol-list command
output to have a space in the front of the line, see:

https://www.redhat.com/archives/libvir-list/2013-November/msg00380.html

Add a strategic ".lstrip()" to the re.search() on the output
Merge pull request #1113 from jferlan/virsh_volume

virsh_volume: Adjust for upstream change