* clean unused code: piece.cc/h

* clean usage

* transfer: string tinyformat errors and part of enforce into pten

* remove comment

* fix by code review

* assert is not compile in -DNDEBUG

* add string as dependences of paddle_inference

* replace boost::algorithm::ends_with with self define ends_with function

* remove BOOST macro in certain operators

* remove boost::lexical_cast

* add test for string_helper

* add more test case for string_helper

* modify join_string func and test case

* fix build_strategy_test failed bug

* remove string_helper_test from parallel_UT_rule.py

test=develop

* wip multi process multi gpu dist training

* workable for p2p

* update test=develop

* change back env name test=develop

* fix alloc init

* fix cpu build test=devlop

* fix mac tests test=develop

* refine code

* refine test=develop

* Make `PADDLE_ENFORCE_EQ` supports custom class, like DDim