virtcontainers: fix kata-agent fail to start

If kata-agent doesn't start in VM, we need to do some rollback
operations to release related resources.

add grpc check() to check kata-agent is running or not

Fixes: #297

Signed-off-by: flyflypeng <jiangpengfei9@huawei.com>

virtcontainers/kata_agent.go

@@ -512,6 +512,11 @@ func (k *kataAgent) startSandbox(sandbox *Sandbox) error {
 		hostname = hostname[:maxHostnameLen]
 	}
 
+	// check grpc server is serving
+	if err = k.check(); err != nil {
+		return err
+	}
+
 	//
 	// Setup network interfaces and routes
 	//