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/golang.org/x/xerrors/doc.go

@@ -0,0 +1,25 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package xerrors implements functions to manipulate errors.
+//
+// This package supports transitioning to the Go 2 proposal for error values:
+//   https://golang.org/design/29934-error-values
+//
+// Most of the functions and types in this package will be incorporated into the
+// standard library's errors package in Go 1.13; the behavior of this package's
+// Errorf function will be incorporated into the standard library's fmt.Errorf.
+// Use this package to get equivalent behavior in all supported Go versions. For
+// example, create errors using
+//
+//    xerrors.New("write failed")
+//
+// or
+//
+//    xerrors.Errorf("while reading: %v", err)
+//
+// If you want your error type to participate in the new formatting
+// implementation for %v and %+v, provide it with a Format method that calls
+// xerrors.FormatError, as shown in the example for FormatError.
+package xerrors // import "golang.org/x/xerrors"