Update install_ubuntu.sh to the new age
Summary:
Ref T4200. Since the last time this script was written, Ubuntu has made lots of changes.
Try to keep up with those.
Test Plan:
Ran this on frash installs of Ubuntu 16.04 LTS and 18.04 LTS (Pre-release).
Got to see Phabricator running.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: amckinley, Korvin
Maniphest Tasks: T4200
Differential Revision: https://secure.phabricator.com/D19394