btrfs: regression test for btrfs incremental send

This is a regression test for a btrfs incremental send issue.
If between two snapshots we rename an existing directory named X to Y and
make it a child (direct or not) of a new inode named X, we were delaying
the move/rename of the former directory unnecessarily, which would result
in attempting to rename the new directory from its orphan name to name X
prematurely. This made btrfs receive fail with an error message like the
following:

   rename o261-7-0 -> merlin/RC/OSD failed

This issue was a regression in the 3.16 kernel and got fixed by the
following linux kernel btrfs patch:

   Btrfs: send, don't delay dir move if there's a new parent inode

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

tests/btrfs/group

@@ -79,3 +79,4 @@
 074 auto defrag remount compress
 075 auto quick subvol
 076 auto quick
+077 auto quick