Fix stale volume list for NetApp 7-mode ISCSI driver

Fix stale volume list for NetApp 7-mode ISCSI driver

While contacting filer through DFM in order to create volume from
snapshot, the operation may fail with an error "No entry in LUN
table for volume". Although the LUN representing the volume was
created on the filer, the LUN list was not refreshed in time, which
 caused an error. This fix handles this situation for creating
volume from snapshots.

Note that this fix adds the requirement that the driver host and
DFM machine should be reasonably time-synchronized.

Fixes bug 1095633

Change-Id: I77fff4c36a3af72d28f2d01988a6067919093718