Discover workflows automatically.

Summary: Most scripts detect the relevant workflows automatically. Some scripts, however, use a hardcoded list of workflows.

Test Plan: Ran ./bin/aphlict, ./bin/cache and ./bin/phd.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9564