use istio client-go library instead of knative (#1661)

use istio client-go library instead of knative
bump kubernetes dependency version
change code coverage to codecov

vendor/k8s.io/apiserver/pkg/util/webhook/error.go

@@ -16,7 +16,11 @@ limitations under the License.
 
 package webhook
 
-import "fmt"
+import (
+	"fmt"
+
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+)
 
 // ErrCallingWebhook is returned for transport-layer errors calling webhooks. It
 // represents a failure to talk to the webhook, not the webhook rejecting a
@@ -32,3 +36,12 @@ func (e *ErrCallingWebhook) Error() string {
 	}
 	return fmt.Sprintf("failed calling webhook %q; no further details available", e.WebhookName)
 }
+
+// ErrWebhookRejection represents a webhook properly rejecting a request.
+type ErrWebhookRejection struct {
+	Status *apierrors.StatusError
+}
+
+func (e *ErrWebhookRejection) Error() string {
+	return e.Status.Error()
+}