static BucketEntry createBucketEntry(long offset, int len) {
    return createBucketEntry(offset, len, ByteBuffAllocator.HEAP);
  }
Override the {@link BucketEntry} so that we can set an arbitrary offset.
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/bucket/TestByteBufferIOEngine.java