Detach volume fails when using multipath iscsi

Enabled multipath for libvirt iscsi volume driver. Attach volume worked,
however, detach volume failed. It failed because it can't find multipath
device "/dev/mapper/xxxxxxxx" from connection_info and block device
mapping table.

The fix is to retrieve multipath device info dynamically at detach time.

Fixes: bug #1178893

Change-Id: I53a3888daef93b57bf7f57438f74cee05e794b52
Fix for missing multipath device name

Due to formatting changes in the multipath -l output
we were sometimes missing the device name for each of the
multipath devices which gave us a device of '/dev/'.  This
causes problems on detach.

Fixes Bug: #1180497

Change-Id: I6017dda149776624fac452140d3d0f5df3f5fd5a
Merge "Detach volume fails when using multipath iscsi"
Merge "Fix for missing multipath device name"