join byid and kern maps instead of picking one (bnc #896665)

If a device doesn't have a by-id link (e.g. vda) it used to be dropped in
GetDeviceMap() as long as there are other devices with by-id links. That's
rather bad. Instead we now use by-id and kernel names so we always have an
entry in device_map.
ensure that device nap hash values (hd0, hd1...) are unique
simplify device map logging
release 0.822
Merge pull request #45 from openSUSE/bnc_896665

join byid and kern maps instead of picking one (bnc #896665)