Move testutils to pkg

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

snapshots/btrfs/btrfs_test.go

@@ -28,9 +28,9 @@ import (
 	"testing"
 
 	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/pkg/testutil"
 	"github.com/containerd/containerd/snapshots"
 	"github.com/containerd/containerd/snapshots/testsuite"
-	"github.com/containerd/containerd/testutil"
 	"github.com/pkg/errors"
 	"golang.org/x/sys/unix"
 )