Switching from crypto/rand to math/rand to avoid blocking

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

diff/walking/differ.go

@@ -18,10 +18,10 @@ package walking
 
 import (
 	"context"
-	"crypto/rand"
 	"encoding/base64"
 	"fmt"
 	"io"
+	"math/rand"
 	"time"
 
 	"github.com/containerd/containerd/archive"

rootfs/apply.go

@@ -18,9 +18,9 @@ package rootfs
 
 import (
 	"context"
-	"crypto/rand"
 	"encoding/base64"
 	"fmt"
+	"math/rand"
 	"time"
 
 	"github.com/containerd/containerd/diff"

services/leases/local.go

@@ -18,9 +18,9 @@ package leases
 
 import (
 	"context"
-	"crypto/rand"
 	"encoding/base64"
 	"fmt"
+	"math/rand"
 	"time"
 
 	"google.golang.org/grpc"