Stop using math/rand.Read and rand.Seed (deprecated in Go 1.20)

From golangci-lint:

> SA1019: rand.Read has been deprecated since Go 1.20 because it
>shouldn't be used: For almost all use cases, crypto/rand.Read is more
>appropriate. (staticcheck)

> SA1019: rand.Seed has been deprecated since Go 1.20 and an alternative
>has been available since Go 1.0: Programs that call Seed and then expect
>a specific sequence of results from the global random source (using
>functions such as Int) can be broken when a dependency changes how
>much it consumes from the global random source. To avoid such breakages,
>programs that need a specific result sequence should use
>NewRand(NewSource(seed)) to obtain a random generator that other
>packages cannot access. (staticcheck)

See also:

- https://pkg.go.dev/math/rand@go1.20#Read
- https://pkg.go.dev/math/rand@go1.20#Seed

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

mount/losetup_linux.go

@@ -19,11 +19,11 @@ package mount
 import (
 	"errors"
 	"fmt"
-	"math/rand"
 	"os"
 	"strings"
 	"time"
 
+	"github.com/containerd/containerd/pkg/randutil"
 	"golang.org/x/sys/unix"
 )
 
@@ -152,7 +152,7 @@ func setupLoop(backingFile string, param LoopParams) (*os.File, error) {
 			// with EBUSY when trying to set it up.
 			if strings.Contains(err.Error(), ebusyString) {
 				// Fallback a bit to avoid live lock
-				time.Sleep(time.Millisecond * time.Duration(rand.Intn(retry*10)))
+				time.Sleep(time.Millisecond * time.Duration(randutil.Intn(retry*10)))
 				continue
 			}
 			return nil, err