test=develop

* random failed. rerun ci. test=develop

* windows failed. rerun ci. test=develop

* show detail error log on ci

* test

* fix memopt and dist

* update apispec

* will fix different batch issue test=develop

* wip

* clean up

* should fix running with memopt

* add ut

* mark lr schedule op role

* hide lr_schedule_guard

* use op_role_var instead of ufind

* unify dist test name

* wip for py3 support

* fix var deref

* fix python3 mem_opt order

* remove comments

* hide program APIs

* fix merge error

* update

Fix pb_protobuf2 FromString problem

* hide variable API

* edit API.spec

* remove block api

* remove clone_variable

* hide block inner apis

* update

* fix tests

* fix mac build error

* enhance memory optimize transpiler to let users set to some skip opt set of variables

* fix range in data flow analysis

* "a piece of job."

* "fix typeo"

* "fix ci"

* fix mac build error

* remove unnecessary build graph

* add memopt level

* add opt level for image classification demo

* clean code

* add delete op

* clean code

* test machine translation demo

* clean code

* clean code

* skip fill constant with force cpu

* clean code

* clean code

* refine code

* clean code

* fix bug

* Add block.fwd_block_id

* fix bug in memory optimization transpiler

* Change DFS to BFS

* Add comments