xfstests: btrfs/016: a hole punching send test

xfstests: btrfs/016: a hole punching send test

I recently added a patch to avoid sending holes with btrfs send, but I screwed
it up by not sending a hole when we did a hole punch.  This is an xfstest
version of the test I wrote to show that I had a bug and to verify I was fixing
it properly.  This test properly fails with my old patch and passes with my good
patch.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>