agent-client: include log in agent client

This file is mainly used by kata-runtime and missing logging part.
We add one new "agent-client" log field here, and Plz notice that,
you should turn on the `kata-runtime` debug option to see the output.

Fixes: #705

Signed-off-by: Penny Zheng <penny.zheng@arm.com>

protocols/client/client.go

@@ -13,6 +13,7 @@ import (
 	"fmt"
 	"net"
 	"net/url"
+	"os"
 	"strconv"
 	"strings"
 	"time"
@@ -21,6 +22,7 @@ import (
 	"github.com/hashicorp/yamux"
 	"github.com/mdlayher/vsock"
 	opentracing "github.com/opentracing/opentracing-go"
+	"github.com/sirupsen/logrus"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
 	grpcStatus "google.golang.org/grpc/status"
@@ -39,6 +41,14 @@ var defaultCloseTimeout = 5 * time.Second
 
 var hybridVSockPort uint32
 
+var agentClientFields = logrus.Fields{
+	"name":   "agent-client",
+	"pid":    os.Getpid(),
+	"source": "agent-client",
+}
+
+var agentClientLog = logrus.WithFields(agentClientFields)
+
 // AgentClient is an agent gRPC client connection wrapper for agentgrpc.AgentServiceClient
 type AgentClient struct {
 	agentgrpc.AgentServiceClient
@@ -414,7 +424,9 @@ func HybridVSockDialer(sock string, timeout time.Duration) (net.Conn, error) {
 		// - [host] CONNECT <port><LF>
 		// - [guest/success] OK <assigned_host_port><LF>
 		reader := bufio.NewReader(conn)
-		if response, err := reader.ReadString('\n'); err != nil {
+		response, err := reader.ReadString('\n')
+		agentClientLog.WithField("response", response).Debug("HybridVsock trivial handshake")
+		if err != nil {
 			conn.Close()
 			return nil, err
 		} else if !strings.Contains(response, "OK") {