replace ioutil with io and os (#2327)

set the go version to 1.16 in pr.yml and tests.yml, so as to be consistent with the version in go.mod.

util/http/http_test.go

@@ -1,7 +1,7 @@
 package http
 
 import (
-	"io/ioutil"
+	"io"
 	"net"
 	"net/http"
 	"testing"
@@ -48,7 +48,7 @@ func TestRoundTripper(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	b, err := ioutil.ReadAll(w.Body)
+	b, err := io.ReadAll(w.Body)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -68,7 +68,7 @@ func TestRoundTripper(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	b, err = ioutil.ReadAll(rsp.Body)
+	b, err = io.ReadAll(rsp.Body)
 	if err != nil {
 		t.Fatal(err)
 	}

util/kubernetes/api/response.go

@@ -4,7 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 )
 
@@ -87,7 +87,7 @@ func newResponse(res *http.Response, err error) *Response {
 		return r
 	}
 
-	b, err := ioutil.ReadAll(r.res.Body)
+	b, err := io.ReadAll(r.res.Body)
 	if err == nil {
 		r.err = errors.New(string(b))
 		return r

util/kubernetes/client/client.go

@@ -6,7 +6,6 @@ import (
 	"crypto/tls"
 	"errors"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"path"
@@ -360,7 +359,7 @@ func NewClusterClient() *client {
 		logger.Fatal(errors.New("service account not found"))
 	}
 
-	token, err := ioutil.ReadFile(path.Join(serviceAccountPath, "token"))
+	token, err := os.ReadFile(path.Join(serviceAccountPath, "token"))
 	if err != nil {
 		logger.Fatal(err)
 	}

util/kubernetes/client/util.go

@@ -6,7 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
+	"os"
 	"strings"
 	"text/template"
 )
@@ -45,7 +45,7 @@ func certificatesFromFile(file string) ([]*x509.Certificate, error) {
 	if len(file) == 0 {
 		return nil, errors.New("error reading certificates from an empty filename")
 	}
-	pemBlock, err := ioutil.ReadFile(file)
+	pemBlock, err := os.ReadFile(file)
 	if err != nil {
 		return nil, err
 	}