btrfs: test power failure after fsync and rename exchanging directories

btrfs: test power failure after fsync and rename exchanging directories

Test renaming one directory over another one that has a subvolume inside
it and fsync a file in the other directory that was previously renamed.
We want to verify that after a power failure we are able to mount the
filesystem and it has the correct content (all renames visible).

This exercises a bug fixed by the following kernel commit:

  7ba0b6461bc4 ("btrfs: always detect conflicting inodes when logging inode refs")

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>