performance/write-behind: Add test case for fd being marked bad after write failures.

BUG: 765473
Change-Id: Ia5d9fecc7f84ee4d51f8037e2dd1ed03f0394bd9
Signed-off-by: Raghavendra G <raghavendra@gluster.com>
Reviewed-on: http://review.gluster.org/4632
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>