Remove dup of LibvirtISCSIVolumeDriver in LibvirtISERVolumeDriver

LibvirtISERVolumeDriver is an almost copy of
LibvirtISCSIVolumeDriver.

Change-Id: I7f71be69df6dc203508114fc67f55b7da2b0e529
Merge "Remove dup of LibvirtISCSIVolumeDriver in LibvirtISERVolumeDriver"