[Bug]Fix race between sandbox.delete() and SetKey()

When sandbox is deleting, another SetKey routine could be also in
progress as there's no lock to protect it, when this happens, there
could be a scene that one sandbox is removed, but it's osSbox file
"/var/run/docker/netns/xxxx" left on system and will never be cleaned.

So add a inDelete check for SetKey() to eliminate the race.

Signed-off-by: Zhang Wei <zhangwei555@huawei.com>

libnetwork/sandbox.go

@@ -626,6 +626,10 @@ func (sb *sandbox) SetKey(basePath string) error {
 	}
 
 	sb.Lock()
+	if sb.inDelete {
+		sb.Unlock()
+		return types.ForbiddenErrorf("failed to SetKey: sandbox %q delete in progress", sb.id)
+	}
 	oldosSbox := sb.osSbox
 	sb.Unlock()