Rename concrete Harbormaster step implementations

Summary: Ref T1049. For consistency, rename these to "Harbormaster...".

Test Plan: Ran migration, ran builds, everything still works fine.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T1049

Differential Revision: https://secure.phabricator.com/D8602