Instead of overloading the constructor and check methods with optional
arguments, expose optional arguments via setters. We are about to add
another one, and this was getting unwieldy.
We still use a Factory to create GerritPublicKeyChecker, which parses
the config once in a @Singleton and subsequently configures all
checkers with that config. Since the checker is initially created when
a store might not be available (because the repo hasn't been opened),
we need to separate the trusted key config setter from the store
setter, and check state at use time.
Change-Id: Ide6bc76a8180f91caa6f03f1a0eb25ec6d20ba45
2737821ae3