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/server/signal.go

@@ -22,6 +22,7 @@ import (
 )
 
 var onlyOneSignalHandler = make(chan struct{})
+var shutdownHandler chan os.Signal
 
 // SetupSignalHandler registered for SIGTERM and SIGINT. A stop channel is returned
 // which is closed on one of these signals. If a second signal is caught, the program
@@ -29,15 +30,30 @@ var onlyOneSignalHandler = make(chan struct{})
 func SetupSignalHandler() <-chan struct{} {
 	close(onlyOneSignalHandler) // panics when called twice
 
+	shutdownHandler = make(chan os.Signal, 2)
+
 	stop := make(chan struct{})
-	c := make(chan os.Signal, 2)
-	signal.Notify(c, shutdownSignals...)
+	signal.Notify(shutdownHandler, shutdownSignals...)
 	go func() {
-		<-c
+		<-shutdownHandler
 		close(stop)
-		<-c
+		<-shutdownHandler
 		os.Exit(1) // second signal. Exit directly.
 	}()
 
 	return stop
 }
+
+// RequestShutdown emulates a received event that is considered as shutdown signal (SIGTERM/SIGINT)
+// This returns whether a handler was notified
+func RequestShutdown() bool {
+	if shutdownHandler != nil {
+		select {
+		case shutdownHandler <- shutdownSignals[0]:
+			return true
+		default:
+		}
+	}
+
+	return false
+}