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/watch/watch.go

@@ -44,6 +44,7 @@ const (
 	Added    EventType = "ADDED"
 	Modified EventType = "MODIFIED"
 	Deleted  EventType = "DELETED"
+	Bookmark EventType = "BOOKMARK"
 	Error    EventType = "ERROR"
 
 	DefaultChanSize int32 = 100
@@ -57,6 +58,10 @@ type Event struct {
 	// Object is:
 	//  * If Type is Added or Modified: the new state of the object.
 	//  * If Type is Deleted: the state of the object immediately before deletion.
+	//  * If Type is Bookmark: the object (instance of a type being watched) where
+	//    only ResourceVersion field is set. On successful restart of watch from a
+	//    bookmark resourceVersion, client is guaranteed to not get repeat event
+	//    nor miss any events.
 	//  * If Type is Error: *api.Status is recommended; other types may make sense
 	//    depending on context.
 	Object runtime.Object