Tests: Disable open-behind

Test assumes that open on the mount point opens the files on bricks
right away.
Change-Id: I94aae857515792e9b694723d30bb085f9e703745
BUG: 821056
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/4540
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>