Modernize the drydock script

Summary: Add a bin/drydock symlink and break it into workflows. Nothing too special here.

Test Plan: Ran bin/drydock wait-for-lease, bin/drydock lease, bin/drydock help, etc.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2015

Differential Revision: https://secure.phabricator.com/D3867