btrfs: test setting the same received UUID to a lot of subvolumes

Test that using the received subvol ioctl to set a received UUID on a root
does not trigger a transaction abort (and turn the filesystem to RO mode)
if a user abuses by assigning the same received UUID to a large number of
subvolumes.

This exercises a bug fixed by the following kernel patch:

 "btrfs: fix transaction abort on set received ioctl due to item overflow"

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