Fixed a problem in iSCSI multipath

Multipathing during copy image to volume and copy volume to image
operations doesn't work properly if there are different targets
associated with different portals for a mulitpath device.

Change-Id: I65c93f3788020c944db0d3a55063a6415554ff11
Closes-Bug: #1266048
(cherry picked from commit 3e4f554f614c8cb6d5f014c72f3c635184a4dec2)
Merge "Fixed a problem in iSCSI multipath" into stable/havana