btrfs-progs: mkfs: add uuid and otime to ROOT_ITEM of, FS_TREE

btrfs-progs: mkfs: add uuid and otime to ROOT_ITEM of, FS_TREE

Currently, the top-level subvolume lacks the UUID. As a result, both
non-snapshot subvolume and snapshot of top-level subvolume do not have
Parent UUID and cannot be distinguisued. Therefore "fi show" of
top-level lists all the subvolumes which lacks the UUID in
"Snapshot(s)" filed.  Also, it lacks the otime information.

Fix this by adding the UUID and otime at the mkfs time.  As a
consequence, snapshots of top-level subvolume now have a Parent UUID and
UUID tree will create an entry for top-level subvolume at mount time.
This should not cause the problem for current kernel, but user program
which relies on the empty Parent UUID may be affected by this change.

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>