btrfs: test incremental send with directory renames

btrfs: test incremental send with directory renames

Test for incremental send where the difference between the parent and
child snapshots is that a directory A was renamed and a directory B was
renamed to the name directory A had before (in the parent snapshot),
but directory A's rename must happen before some other directory C is
renamed.

This issue was fixed by the following linux kernel btrfs patch:

  Btrfs: incremental send, don't rename a directory too soon

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Dave Chinner <david@fromorbit.com>