recovery: fix volmgr cleaning up

 * Don't reset pointer to netlink manager
 * Delete disks in stop() rather then in ~VolumeManager
 * Call destroy() before deleting disks cause delete expects the
   disk to be destroyed
 * Clear the lists or we would read garbage data on the next scan

Change-Id: Idadfa1f33b7cb5f2f3c780848a99344a6608420e