Worker - supporting running queued tasks in process

Summary: Ref D8930. My "send test" for SMS was failing before this patch, and now it works nicely.

Test Plan: Used new code in D8930 that uses $this->queueTask() to get some work done and it got done in process

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9018