default void preUpdateRegionServerConfiguration(
    ObserverContext<RegionServerCoprocessorEnvironment> ctx, Configuration preReloadConf)
    throws IOException {
  }
Called before reloading the RegionServer's {@link Configuration} from disk
@param ctx           the coprocessor instance's environment
@param preReloadConf the {@link Configuration} in use prior to reload
@throws IOException if you need to signal an IO error
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/RegionServerObserver.java