Remove duplication of ISCSIDriver in ISERDriver

ISERDriver is almost copy of ISCSIDriver.

Change-Id: I22394c7a3b26b140b19f76e052c98d11ec59145c
Nexenta iSCSI driver: extend volume stats of _update_volume_stats

Added location_info to stats provided by _update_volume_stats method
of Nexenta iSCSI volume driver.

Change-Id: Ib947180cb6d08d7639443a8998190ab911d1a4a4
Merge "Remove duplication of ISCSIDriver in ISERDriver"
Merge "Nexenta iSCSI driver: extend volume stats of _update_volume_stats"