NetApp NFS: Do not reference dst_img_local before assignment

This patch moves the assignment of the dst_img_local variable to before the
try/finally block that references it so that the finally block will have this
variable no matter where in the try block an error is raised.

Change-ID: Iab48b46559f18a3d6b044abe4bc3e615e7fee075
Closes-Bug: 1309047
(cherry-picked from commit 48a53d32ee243d80b034b38e292e9bfb4b66f881)
Merge "NetApp NFS: Do not reference dst_img_local before assignment" into stable/icehouse