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/apimachinery/pkg/apis/meta/v1/duration.go

@@ -48,3 +48,13 @@ func (d *Duration) UnmarshalJSON(b []byte) error {
 func (d Duration) MarshalJSON() ([]byte, error) {
 	return json.Marshal(d.Duration.String())
 }
+
+// OpenAPISchemaType is used by the kube-openapi generator when constructing
+// the OpenAPI spec of this type.
+//
+// See: https://github.com/kubernetes/kube-openapi/tree/master/pkg/generators
+func (_ Duration) OpenAPISchemaType() []string { return []string{"string"} }
+
+// OpenAPISchemaFormat is used by the kube-openapi generator when constructing
+// the OpenAPI spec of this type.
+func (_ Duration) OpenAPISchemaFormat() string { return "" }