This patch renames the libvirt conf section entry of
iscsi_use_multipath to volume_use_multipath. Both iSCSI and
FibreChannel libvirt volume drivers use this value to determine
if multipath volume attachments are to be used. It's an n-cpu system
wide value that's not specific to iSCSI.
Change-Id: Iebbac91a74df468d5be9b2e70560d5b4394ce595
Closes-Bug: #1593860