R1:26d62ee45018

[Ubuntu Install Script] Automatically enable mod_rewrite

Summary: I needed to figure out how to do this, and it took a couple of minutes.

Test Plan: ran that command on my Ubuntu 12.04 system

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3479