xfstests: btrfs/008, another send regression test

This is a regression test for a problem we had where we'd assume we had created
a directory if it only had subvols inside of it.  This was happening because
subvols would have lower inode numbers than our current send progress because
their inode numbers are based off of a different counter.  Thanks,

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

[rjohnston: renumbered test from 002 to 008]

tests/btrfs/008.out

@@ -0,0 +1,2 @@
+QA output created by 008
+Silence is golden