Move resource allocation to task queue

Summary: Run the actual resource allocation for Drydock out-of-process via the
task queue.

Test Plan: Ran "drydock_control.php", saw it insert a task and wait for task
completion. Ran "phd debug taskmaster" and saw it run the task.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1470