refactor: move from io/ioutil to io and os package

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

content/testsuite/testsuite.go

@@ -21,7 +21,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math/rand"
 	"os"
 	"runtime"
@@ -104,7 +103,7 @@ func makeTest(t *testing.T, name string, storeFn func(ctx context.Context, root
 		ctx := context.WithValue(context.Background(), nameKey{}, name)
 		ctx = logtest.WithT(ctx, t)
 
-		tmpDir, err := ioutil.TempDir("", "content-suite-"+name+"-")
+		tmpDir, err := os.MkdirTemp("", "content-suite-"+name+"-")
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -782,7 +781,7 @@ func checkSmallBlob(ctx context.Context, t *testing.T, store content.Store) {
 	}
 	defer ra.Close()
 	r := io.NewSectionReader(ra, 0, readSize)
-	b, err := ioutil.ReadAll(r)
+	b, err := io.ReadAll(r)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -1080,7 +1079,7 @@ func createContent(size int64) ([]byte, digest.Digest) {
 	// test runs. An atomic integer works just good enough for this.
 	seed := atomic.AddInt64(&contentSeed, 1)
 
-	b, err := ioutil.ReadAll(io.LimitReader(rand.New(rand.NewSource(seed)), size))
+	b, err := io.ReadAll(io.LimitReader(rand.New(rand.NewSource(seed)), size))
 	if err != nil {
 		panic(err)
 	}