Summary: Fixes T4149. This could be a little cleaner (configurable time limits, explicit timeout errors) but stop the major case of looping/infinite commands.
Test Plan: Added `sleep 5 &&` and set timeout to 1, saw an error + kill.
Reviewers: btrahan, skyronic
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T4149
Differential Revision: https://secure.phabricator.com/D7651