pkg: remove random package

The unnecessary `random` package has been removed in favor of using the
`math/rand` package directly. Seeding of the random value from crypto
has been added to the `stringid` package to account for the change.

May need to add an equivalent seed to `namesgenerator`, but this is
often used with `stringid` and has collision protection.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
Upstream-commit: 66cfe61f71252f528ddb458d554cd241e996d9f1
Component: engine

components/engine/pkg/stringutils/stringutils.go

@@ -5,8 +5,6 @@ import (
 	"bytes"
 	"math/rand"
 	"strings"
-
-	"github.com/docker/docker/pkg/random"
 )
 
 // GenerateRandomAlphaOnlyString generates an alphabetical random string with length n.
@@ -15,7 +13,7 @@ func GenerateRandomAlphaOnlyString(n int) string {
 	letters := []byte("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
 	b := make([]byte, n)
 	for i := range b {
-		b[i] = letters[random.Rand.Intn(len(letters))]
+		b[i] = letters[rand.Intn(len(letters))]
 	}
 	return string(b)
 }