Should start with sudo and fallback to su

[Didier Raboud]

HPLIP currently uses a distribution list to determine if `sudo` or `su` should be used.

This is very fragile and doesn't work at the distribution level such as on Debian where sudo is not installed by default but still in vast use. With that in place, I can't use hp-plugin successfully as it will use su, although I don't have a `root` password at all. Also, it doesn't seem to be configurable at all.

I suggest that hplip should really get rid of its distribution list and rather use a "sudo first, then su" approach, which seems much more robust: detect if the sudo executable exists (good baseline for a working `sudo`), then propose to fallback on `su` after three failed attempts.