clean up channel

test=release/1.0.0

(cherry picked from commit 425a8821)

* hide operator API

* update

* update api.spec

* fix merge

* fix test

* 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

In the future, we'd like to encourage user to save
everything during training.
This allows us to
1. Do more flexible optimization passes
2. Re-train and fune-tune

* hide program APIs

* fix merge error

* update

* Support int8 type.

This reverts commit b2df1700.

* dist transpiler add control dependency var between send and recv

* fix async deps

* follow comments and refine

* fix deps connect for rpc ops

* Add Python Callstacks when Op::Run error

* Skip op with sub-block

* refactor: refine callstack info's format

* Reshape only support matrix

* Polish Python code

* Fix UT

* Fix Py3

add export_for_deployment flag to save_inference_model

Fix pb_protobuf2 FromString problem

Fix str and bytes problem
Fix sorted problem
Fix math problem
Fix CI problem

* hide variable API

* edit API.spec