logilab-devtools #111585 lgp shouldn't assume too much about which distributions exist [done]

since the actual work is done by pbuilder or debootstrap (and soon mock) we should let them worry about what are valid distributions

prioritynormal
typeenhancement
done in0.21.0
load0.250
load left0.000
closed by#c67cc14376ed utils: don't try to filter the user's distro list by guessing which are valid