Migrate "Run Command" to use Drydock hosts

Summary: This migrates the "Run Remote Command" build step over to use Drydock hosts and Harbormaster artifacts.

Test Plan:
Created a build plan with a "Lease Host" step and a "Run Command" step. Configured the "Run Command" step to use the artifact from the "Lease Host" step.

Saw the results:

{F87377}

{F87378}

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T1049, T4111

Differential Revision: https://secure.phabricator.com/D7707