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/api/authentication/v1/generated.proto

@@ -84,7 +84,10 @@ message TokenRequestSpec {
   optional int64 expirationSeconds = 4;
 
   // BoundObjectRef is a reference to an object that the token will be bound to.
-  // The token will only be valid for as long as the bound objet exists.
+  // The token will only be valid for as long as the bound object exists.
+  // NOTE: The API server's TokenReview endpoint will validate the
+  // BoundObjectRef, but other audiences may not. Keep ExpirationSeconds
+  // small if you want prompt revocation.
   // +optional
   optional BoundObjectReference boundObjectRef = 3;
 }