Limit max backoff delay to 2 seconds for GRPC connection

Docker use default GRPC backoff strategy to reconnect to containerd when
connection is lost. and the delay time grows exponentially, until reaches 120s.

So Change the max delay time to 2s to avoid docker and containerd
connection failure.

Signed-off-by: Wentao Zhang <zhangwentao234@huawei.com>
(cherry picked from commit d3d8c77d195ce74f36ae6eee24578b9cac48f897)
Signed-off-by: Andrew Hsu <andrewhsu@docker.com>

components/engine/libcontainerd/remote_unix.go

@@ -96,11 +96,13 @@ func New(stateDir string, options ...RemoteOption) (_ Remote, err error) {
 
 	// don't output the grpc reconnect logging
 	grpclog.SetLogger(log.New(ioutil.Discard, "", log.LstdFlags))
-	dialOpts := append([]grpc.DialOption{grpc.WithInsecure()},
+	dialOpts := []grpc.DialOption{
+		grpc.WithInsecure(),
+		grpc.WithBackoffMaxDelay(2 * time.Second),
 		grpc.WithDialer(func(addr string, timeout time.Duration) (net.Conn, error) {
 			return net.DialTimeout("unix", addr, timeout)
 		}),
-	)
+	}
 	conn, err := grpc.Dial(r.rpcAddr, dialOpts...)
 	if err != nil {
 		return nil, fmt.Errorf("error connecting to containerd: %v", err)