agent: mark agent dead when failing to connect

Whenever we fail to connect, do not make any more attempts.
More attempts are possible during cleanup phase but we should
not try to connect any more there.

Signed-off-by: Peng Tao <bergwolf@hyper.sh>

virtcontainers/kata_agent.go

@@ -136,6 +136,7 @@ type kataAgent struct {
 	keepConn       bool
 	proxyBuiltIn   bool
 	dynamicTracing bool
+	dead           bool
 
 	vmSocket interface{}
 	ctx      context.Context
@@ -1581,6 +1582,9 @@ func (k *kataAgent) statsContainer(sandbox *Sandbox, c Container) (*ContainerSta
 }
 
 func (k *kataAgent) connect() error {
+	if k.dead {
+		return errors.New("Dead agent")
+	}
 	// lockless quick pass
 	if k.client != nil {
 		return nil
@@ -1599,6 +1603,7 @@ func (k *kataAgent) connect() error {
 	k.Logger().WithField("url", k.state.URL).Info("New client")
 	client, err := kataclient.NewAgentClient(k.ctx, k.state.URL, k.proxyBuiltIn)
 	if err != nil {
+		k.dead = true
 		return err
 	}