cr: get pid from criu notify when restore

[Ace-Tang]

when restore container from a checkpoint directory, we should get
pid from criu notify, since c.initProcess has not been created.

Signed-off-by: Ace-Tang aceapril@126.com

why I do this

I fail to update runc version in pouch project, AliyunContainerService/pouch#2516, I check the restore code, in criuNotifications function, currentOCIState() can not get pid since c.initProcess has not been created.

    case notify.GetScript() == "setup-namespaces":
        if c.config.Hooks != nil {
            s, err := c.currentOCIState()
            if err != nil {
                return nil
            }

I do not figure out how criu notify can get pid, I want invite @avagin and @adrianreber help to check whether the fix in pr is correct.

[adrianreber]

So it seems #1741 is the reason for the problem. That PR basically removes, by calling out to a new function, that s.Pid is set.

I also see in #1741 that at a few places s.Pid is set just like it is done in this PR.

So it seems that this PR is doing the right thing. 👍

[Ace-Tang]

Thanks @adrianreber

[cyphar]

LGTM, seems reasonable.

[crosbymichael]

LGTM