Adds sudo user to worker info when available

Many of the jobs I use have to be run as hadoop, so it's impossible to tell from
the user who actually ran the job. This adds sudo_user to the worker info so
that it's easier to tell who's running what. This is very handy when I need to
figure out why a large backfill or test job is running if it's causing a lot of
errors or hogging all the resources.
Merge pull request #487 from Houzz/sudo_user

Adds sudo user to worker info when available