Alias is now a fully qualified hardware registry key

There is no need to try to find the device and instance from the alias
software key as it is trivial to parse it out of the hardware key. This
means less work here and more work in the xennet co-installer, which is
the right place for it.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Merge pull request #17 from pauldu/ca-122017

Alias is now a fully qualified hardware registry key