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/endpoints/discovery/storageversionhash.go

@@ -0,0 +1,40 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package discovery
+
+import (
+	"crypto/sha256"
+	"encoding/base64"
+)
+
+// StorageVersionHash calculates the storage version hash for a
+// <group/version/kind> tuple.
+// WARNING: this function is subject to change. Clients shouldn't depend on
+// this function.
+func StorageVersionHash(group, version, kind string) string {
+	gvk := group + "/" + version + "/" + kind
+	if gvk == "" {
+		return ""
+	}
+	bytes := sha256.Sum256([]byte(gvk))
+	// Assuming there are N kinds in the cluster, and the hash is X-byte long,
+	// the chance of colliding hash P(N,X) approximates to 1-e^(-(N^2)/2^(8X+1)).
+	// P(10,000, 8) ~= 2.7*10^(-12), which is low enough.
+	// See https://en.wikipedia.org/wiki/Birthday_problem#Approximations.
+	return base64.StdEncoding.EncodeToString(
+		bytes[:8])
+}