Modernize Drydock CLI management of task execution

Summary:
Ref T2015. Currently, Drydock has a wait-for-lease workflow which is invoked in the background by the lease workflow.

The goal of this mechanism is to allow bin/drydock lease to print out logs as the lease is acquired. However, this predates the runAllTasksInProcess flags, and they provide a simpler and more robust way (potentially with --trace and PhutilConsole) to do synchronous execution and debug logging.

Simplify this whole mechanism: just run everything in-process in bin/drydock lease, and do logging via --trace. We could thread a PhutilConsole through things too, but this seems good enough for now.

Also various cleanup/etc.

Test Plan: Ran bin/drydock lease. Ran bin/harbormaster build X --plan Y, for Y being a Drydock-dependent build plan.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2015

Differential Revision: https://secure.phabricator.com/D7835