Pip install support

[wangkuiyi]

@reyoung had been working on this. He noticed that the manylinux standard requires that wheel packages (or pip packages) must be built on CentOS 5. However, CentOS 5 is too old a Linux distribution whose kernel doesn't support Golang.

@helinwang reminded that if we are to distribute pip packages of PaddlePaddle, we can simply disable Golang during building (cmake WITH_GO=OFF) because currently Golang is only used with the parameter server and in our future plan we are not going to have the parameter server.

[reyoung]

Related issue #4050
It seems that @typhoonzero found a new docker image which based on CentOS6.

[Yancey1989]

I'll close this issue since we have already support pip install paddlepaddle.