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