Fix ISCSIDriver rescan.

Cinder fails to rescan iSCSI targets after running copy_image_to_volume
or copy_volume_to_image with the generic iSCSI implementation, due to
a missing comma.

Change-Id: I726e8da1f0221e47bae2593e03bc88a47c487814
Fixes: bug 1144591
Merge "Fix ISCSIDriver rescan."