*  fix mkdir conflict

*  fix load/save lookup tables

 test=develop

* add lookup_table_utils

* fix load optimize vars on pserver

* delete lookup table utils

* fix save and load lookup tables

* fix load optimizer var

* fix load optimizer var, test=develop

* fix python 3 style, test=develop

* move lookup_table_utils to contrib utils

Optimize selected rows for dist lookup table with rwlock 

Do not use ctor

* Reduce line of codes.
* We can use virtual function for Maker now.
* The implementation does not care what maker holds, it is easier to
refactor later.