add '--snapshotter-labels' in ctr run and ctr c create
which can pass labels to snappshotter on preparing new
snapshot.
Pass command label to snapshotter can help it determine
which kind of writable snapshots should be provide.
For some snapshotter, such as overlaybd:
( https://github.com/alibaba/accelerated-container-image ),
it can provide 2 kind of writable snapshot (overlayfs dir or
blockdevice) by command label values.
Signed-off-by: Yifan Yuan <tuji.yyf@alibaba-inc.com>
bda7b58666