Btrfs-progs: make send/receive compatible with older kernels

Btrfs-progs: make send/receive compatible with older kernels

Some users complaint that with latest btrfs-progs, they will
fail to use send/receive. The problem is new tool will try
to use uuid tree while it dosen't work on older kernel.

Now we first check if we support uuid tree, if not we fall into
normal search as previous way.i copy most of codes from Alexander
Block's previous codes and did some adjustments to make it work.

Signed-off-by: Alexander Block <ablock84@googlemail.com>
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>