btrfs: test send after radical changes in a complex directory hierarchy

btrfs: test send after radical changes in a complex directory hierarchy

Test an incremental send operation in a scenario where the relationship
of ancestor-descendant between multiple directories is inversed, and
where multiple directories that were previously ancestors of another
directory now become descendents of multiple directories that used to be
their ancestors in the parent snapshot. This used to trigger an
infinite loop in the kernel code.

This is motivated by a bug found in btrfs which is fixed by the following
patch for the linux kernel:

  "Btrfs: send, fix infinite loop due to directory rename dependencies"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>