@Override
  public CompletableFuture<Boolean> bulkLoad(TableName tableName,
    List<Pair<byte[], String>> familyPaths, byte[] row, boolean assignSeqNum, Token<?> userToken,
    String bulkToken, boolean copyFiles, List<String> clusterIds, boolean replicate) {
    return null;
  }
Can be overridden in UT if you only want to implement part of the methods in
{@link AsyncClusterConnection}.
hbase-server/src/test/java/org/apache/hadoop/hbase/client/DummyAsyncClusterConnection.java