Delete the disk device manager when done. This is not only good practice, but also allows the manager to unpublish all partitions.

git-svn-id: file:///srv/svn/repos/haiku/trunk/current@3512 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/tests/kernel/core/disk_device_manager/DiskDeviceManagerTest.cpp

@@ -17,6 +17,7 @@ main()
 	KDiskDeviceManager::CreateDefault();
 	KDiskDeviceManager *manager = KDiskDeviceManager::Default();
 	manager->InitialDeviceScan();
+	KDiskDeviceManager::DeleteDefault();
 	return 0;
 }