default void preCommitStoreFile(ObserverContext<? extends RegionCoprocessorEnvironment> ctx,
    byte[] family, List<Pair<Path, Path>> pairs) throws IOException {
  }
Called before moving bulk loaded hfile to region directory.
@param ctx    the environment provided by the region server
@param family column family
@param pairs  List of pairs of { HFile location in staging dir, HFile path in region dir } Each
              pair are for the same hfile.
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/RegionObserver.java