support checkpoint without committing a checkpoint dir into a
checkpoint image and restore without untar image into checkpoint
directory. support for both v1 and v2 runtime
Signed-off-by: Ace-Tang <aceapril@126.com>
when use `ctr t checkpoint`, runtime name should get from container
info, but not passed by flag, since task has already running with
specified runtime
Signed-off-by: Ace-Tang <aceapril@126.com>
