There are currently to options that determine whether a Gerrit instance
is a replica: container.slave (deprecated) or container.replica. Thus,
currently each plugin has to take care itself to test both options to
determine, if the instance is a replica or not.
This change adds the computation whether an instance is a replica to
Gerrit core and adds an annotation that plugins can inject.
Change-Id: I7c6de778c265f3526091cc4be296460fe82e6891
c4e5c07d08