Added some more unittest cases for fs_utils file.

Change-Id: I4c13fd7b3d6c21389b701437dd4a4a5cd0a31212
Signed-off-by: Mohammed Junaid <junaid@redhat.com>
Reviewed-on: http://review.gluster.org/5065
Reviewed-by: Peter Portante <pportant@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>
Reviewed-by: Luis Pabon <lpabon@redhat.com>