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/github.com/go-openapi/errors/auth.go

@@ -14,7 +14,9 @@
 
 package errors
 
+import "net/http"
+
 // Unauthenticated returns an unauthenticated error
 func Unauthenticated(scheme string) Error {
-	return New(401, "unauthenticated for %s", scheme)
+	return New(http.StatusUnauthorized, "unauthenticated for %s", scheme)
 }