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/client-go/tools/cache/mutation_cache.go

@@ -42,6 +42,7 @@ type MutationCache interface {
 	Mutation(interface{})
 }
 
+// ResourceVersionComparator is able to compare object versions.
 type ResourceVersionComparator interface {
 	CompareResourceVersion(lhs, rhs runtime.Object) int
 }