refactor: move from io/ioutil to io and os packages (#5266)

The io/ioutil package has been deprecated as of Go 1.16 [1]. This commit
replaces the existing io/ioutil functions with their new definitions in
io and os packages.

[1]: https://golang.org/doc/go1.16#ioutil
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

pkg/simple/client/kiali/mock_client.go

@@ -2,7 +2,7 @@ package kiali
 
 import (
 	"bytes"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/url"
 )
@@ -15,13 +15,13 @@ type MockClient struct {
 func (c *MockClient) Do(req *http.Request) (*http.Response, error) {
 	return &http.Response{
 		StatusCode: 200,
-		Body:       ioutil.NopCloser(bytes.NewReader([]byte(c.RequestResult))),
+		Body:       io.NopCloser(bytes.NewReader([]byte(c.RequestResult))),
 	}, nil
 }
 
 func (c *MockClient) PostForm(url string, data url.Values) (resp *http.Response, err error) {
 	return &http.Response{
 		StatusCode: 200,
-		Body:       ioutil.NopCloser(bytes.NewReader(c.TokenResult)),
+		Body:       io.NopCloser(bytes.NewReader(c.TokenResult)),
 	}, nil
 }