Generate a node-specific UUID

Certain batches of Dell and IBM hardware seems to
have the same hardware product UUID. As libvirtd
requires a globally unique identifier for live
migration, lets create one on our own.

(cherry picked from commit d886aa52122ce04bfea0820ea35d746ec492e9ad)
Merge pull request #317 from dirkmueller/release/pebbles/master

Generate a node-specific UUID