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/admission/initializer/interfaces.go

@@ -17,7 +17,6 @@ limitations under the License.
 package initializer
 
 import (
-	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apiserver/pkg/admission"
 	"k8s.io/apiserver/pkg/authorization/authorizer"
 	"k8s.io/client-go/informers"
@@ -41,9 +40,3 @@ type WantsAuthorizer interface {
 	SetAuthorizer(authorizer.Authorizer)
 	admission.InitializationValidator
 }
-
-// WantsScheme defines a function that accepts runtime.Scheme for admission plugins that need it.
-type WantsScheme interface {
-	SetScheme(*runtime.Scheme)
-	admission.InitializationValidator
-}