gluster: Corrected the status values

VDSM returns as IN_PROGRESS and NOT_STARTED for the tasks which are in
progress and not started yet respectively.
Corrected the same in engine code.

Change-Id: Iaa2b66a2f11270d5b02accded8f8fd74c226ccfe
Signed-off-by: Shubhendu Tripathi <shtripat@redhat.com>