Reuse a single DeviceSetDM for all the tests

We wrap the "real" DeviceSet for each test so that we get only
a single device-mapper pool and loopback mounts, but still
separate out the IDs in the tests. This makes the test run
much faster.

runtime_test.go

@@ -457,7 +457,7 @@ func TestRestore(t *testing.T) {
 
 	// Here are are simulating a docker restart - that is, reloading all containers
 	// from scratch
-	runtime2, err := NewRuntimeFromDirectory(runtime1.root, devmapper.NewDeviceSetDM(runtime1.root), false)
+	runtime2, err := NewRuntimeFromDirectory(runtime1.root, runtime1.deviceSet, false)
 	if err != nil {
 		t.Fatal(err)
 	}

utils_test.go

@@ -2,7 +2,7 @@ package docker
 
 import (
 	"github.com/dotcloud/docker/utils"
-	"github.com/dotcloud/docker/devmapper"
+	"path/filepath"
 	"io"
 	"io/ioutil"
 	"os"
@@ -43,7 +43,7 @@ func newTestRuntime() (*Runtime, error) {
 		return nil, err
 	}
 
-	runtime, err := NewRuntimeFromDirectory(root, devmapper.NewDeviceSetDM(root), false)
+	runtime, err := NewRuntimeFromDirectory(root, NewDeviceSetWrapper (globalRuntime.deviceSet, filepath.Base(root)), false)
 	if err != nil {
 		return nil, err
 	}