Make Harbormaster buildable status more of a nice flexible map and less of a bunch of switch statements

Summary: Depends on D19063. Ref T13054. Prepare for the addition of a new PREPARING status by getting rid of the "scattered mess of switch statements" pattern of status management.

Test Plan: Searched/browsed buildables. Viewed buildables. Viewed revisions. Grepped for all affected symbols.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13054

Differential Revision: https://secure.phabricator.com/D19064