btrfs: test sending snapshots received from other filesystems

btrfs: test sending snapshots received from other filesystems

Test that sending a snapshot received from a different filesystem is
possible for both full and incremental send operations.

This used to work until the linux kernel release 4.2, but a commit [1] in
that release introduced a regression which did not allow this anymore.

The regression is fixed by the linux kernel patch titled:

  "btrfs: fix resending received snapshot with parent"

[1] 37b8d27de5d0 ("Btrfs: use received_uuid of parent during send")

Cc: Josef Bacik <jbacik@fb.com>
Cc: Robin Ruede <rruede+git@gmail.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>