public Optional<ApplicationReindexing> readReindexingStatus(ApplicationId id) {
        return curator.getData(reindexingDataPath(id))
                      .map(ReindexingStatusSerializer::fromBytes);
    }
List the active applications of a tenant in this config server.

@return a list of {@link ApplicationId}s that are active.
configserver/src/main/java/com/yahoo/vespa/config/server/application/ApplicationCuratorDatabase.java