Fix antctl trace-packet arguments missing issue

Fix the following error when running `antctl trace-packet`, which is
caused by missing arguments for ovs-appctl command.

```
syntax error at br-int (or the bridge name was omitted)
ovs-appctl: /var/run/openvswitch/ovs-vswitchd.103.ctl: server returned an error
```

Signed-off-by: Lan Luo <luola@vmware.com>

pkg/agent/apiserver/handlers/ovstracing/handler.go

@@ -76,7 +76,7 @@ func getServiceClusterIP(aq querier.AgentQuerier, name, namespace string) (net.I
 		if k8serrors.IsNotFound(err) {
 			return nil, handlers.NewHandlerError(errors.New("Service not found"), http.StatusNotFound)
 		}
-		klog.Errorf("Failed to get Service from Kubernetes API: %v", err)
+		klog.ErrorS(err, "Failed to get Service from Kubernetes API")
 		return nil, handlers.NewHandlerError(errors.New("Kubernetes API error"), http.StatusInternalServerError)
 	}
 	return net.ParseIP(srv.Spec.ClusterIP).To4(), nil
@@ -127,7 +127,7 @@ func getPeerAddress(aq querier.AgentQuerier, peer *tracingPeer, addrFamily uint8
 			err := handlers.NewHandlerError(fmt.Errorf("Pod %s/%s not found", peer.namespace, peer.name), http.StatusNotFound)
 			return nil, nil, err
 		}
-		klog.Errorf("Failed to get Pod from Kubernetes API: %v", err)
+		klog.ErrorS(err, "Failed to get Pod from Kubernetes API")
 		return nil, nil, handlers.NewHandlerError(errors.New("Kubernetes API error"), http.StatusInternalServerError)
 	}
 	// Return IP only assuming it should be a remote Pod.
@@ -356,7 +356,7 @@ func validateRequest(r *http.Request) (*request, *handlers.HandlerError) {
 	return &request, nil
 }
 
-// HandleFunc returns the function which can handle API requests to "/ovsflows".
+// HandleFunc returns the function which can handle API requests to "/ovstracing".
 func HandleFunc(aq querier.AgentQuerier) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		var traceReq *ovsctl.TracingRequest
@@ -380,9 +380,11 @@ func HandleFunc(aq querier.AgentQuerier) http.HandlerFunc {
 				// ovs-appctl has been executed but returned an error (e.g. the provided
 				// "flow" expression is incorrect). Return the error output to the client in
 				// this case.
-				out = execErr.GetErrorOutput()
+				klog.ErrorS(execErr, "Tracing command failed")
+				http.Error(w, execErr.GetErrorOutput(), http.StatusInternalServerError)
+				return
 			} else {
-				klog.Errorf("Failed to execute tracing command: %v", err)
+				klog.ErrorS(err, "Failed to execute tracing command")
 				http.Error(w, "failed to execute tracing command", http.StatusInternalServerError)
 				return
 			}

pkg/agent/apiserver/handlers/ovstracing/handler_test.go

@@ -20,6 +20,8 @@ import (
 	"net"
 	"net/http"
 	"net/http/httptest"
+	"os"
+	"os/exec"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -78,6 +80,7 @@ type testCase struct {
 	query          string
 	calledTrace    bool
 	expectedStatus int
+	execErr        *ovsctl.ExecError
 }
 
 func TestPodFlows(t *testing.T) {
@@ -197,6 +200,26 @@ func TestPodFlows(t *testing.T) {
 			calledTrace:    true,
 			expectedStatus: http.StatusOK,
 		},
+		{
+			test:           "Mock syntax error",
+			query:          "",
+			calledTrace:    true,
+			expectedStatus: http.StatusInternalServerError,
+			execErr: ovsctl.NewExecError(&exec.ExitError{
+				ProcessState: &os.ProcessState{},
+				Stderr:       []byte("syntax error"),
+			}, "server returned an error"),
+		},
+		{
+			test:           "Mock command exec error",
+			query:          "",
+			calledTrace:    true,
+			expectedStatus: http.StatusInternalServerError,
+			execErr: ovsctl.NewExecError(&exec.Error{
+				Name: "fake err",
+				Err:  errors.New("command not run correctly"),
+			}, "server returned an error"),
+		},
 	}
 	for i := range testcases {
 		tc := testcases[i]
@@ -243,7 +266,7 @@ func TestPodFlows(t *testing.T) {
 				if tc.expectedStatus == http.StatusOK {
 					ctl.EXPECT().Trace(gomock.Any()).Return(testTraceResult, nil).Times(1)
 				} else {
-					ctl.EXPECT().Trace(gomock.Any()).Return(nil, errors.New("tracing error")).Times(1)
+					ctl.EXPECT().Trace(gomock.Any()).Return("", tc.execErr).Times(1)
 				}
 			}
 		} else {

pkg/ovs/ovsctl/appctl.go

@@ -38,10 +38,11 @@ func (r *ovsAppctlRunner) RunAppctlCmd(cmd string, needsBridge bool, args ...str
 	if needsBridge {
 		cmdArgs = append(cmdArgs, r.bridge)
 	}
+	cmdArgs = append(cmdArgs, args...)
 	ovsCmd := exec.CommandContext(context.TODO(), "ovs-appctl", cmdArgs...)
 	out, err := ovsCmd.CombinedOutput()
 	if err != nil {
-		return nil, newExecError(err, string(out))
+		return nil, NewExecError(err, string(out))
 	}
 	return out, nil
 }

pkg/ovs/ovsctl/ovsctl.go

@@ -261,7 +261,7 @@ func newBadRequestError(msg string) BadRequestError {
 	return BadRequestError(msg)
 }
 
-func newExecError(err error, errorOutput string) *ExecError {
+func NewExecError(err error, errorOutput string) *ExecError {
 	e := &ExecError{error: err}
 	if e.CommandExecuted() {
 		e.errorOutput = errorOutput