Show Drydock resource leases, add DrydockLeaseQuery, allow reuse of working copies

Summary: Minor updates to Drydock things to make them work better. In particular, after this patch working copies are correctly allocated or reused.

Test Plan: Ran "reparse.php --harbormaster <derp derp>", saw reuse of working copies when unleased resources were avilable.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2015

Differential Revision: https://secure.phabricator.com/D4216