private RegionServerStartupResponse.Builder
    addConfig(final RegionServerStartupResponse.Builder resp, final String key) {
    NameStringPair.Builder entry =
      NameStringPair.newBuilder().setName(key).setValue(server.getConfiguration().get(key));
    resp.addMapEntries(entry.build());
    return resp;
  }
@return Subset of configuration to pass initializing regionservers: e.g. the filesystem to use
        and root directory to use.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/MasterRpcServices.java