engine: gluster cifs - use enable/disable

Exporting gluster volumes through CIFS/SMB is controlled
by the user.cifs volume option. gluster expects the values
for this option should be enable or disable instead on/off.

Change-Id: I505013e47f5905f3c679ac099a6a8163c9d12071
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>