Investigate gosu for stepping down from root to chef

[lgrosz]

Right now fixuid is used to step down to an unprivileged user. The docker documentation mentions gosu for this use-case. Something fixuid does is set the uid:gid of chef to the ones provided in the -u flag. It also chowns all the directories previously owned by 1000:1000. This is extremely useful, but if an docker-approved solution works as well, I'd like to use it.