Update drubuntu to work with drush 5

Drush 5 introduces some changes in engines definition that breaks compatibility with drubuntu. See #1399934: Engines TNG for reference.

Engine types now must be declared in a new hook and engines definition has also changed. Attached patch is just a start.

I'm not myself a drubuntu user so I need to set up two virtual machines to see drubuntu working and complete this task.