Currently, WITH_GOLANG is a compiling flag, and not all Paddle binary
enable `WITH_GOLANG=ON`. So we cannot ensure that every paddle has
`master.so`. Make load that C libary lazily could let the user run
Paddle without `WITH_GOLANG=ON`.

* using etcd as fault tolerant training

* update

* workable version, ft not tested

* small fix

* update

* remove TODO