Consolidating TensorFlow CPU and GPU pip packages for release 1.15.0

[Yifei Feng]

Hi all,

We are going to consolidate the GPU and CPU pip packages for 1.15.0 release as proposed before in the group. As a result, `tensorflow` pip package will by default include GPU support (same as `tensorflow-gpu` now) for the platforms we currently have GPU support. It will work on machines with and without Nvidia GPUs. We will continue uploading `tensorflow-gpu` packages, and also provide the CPU only packages at `tensorflow-cpu` for users who are concerned about package size.

This pip package naming change is only for 1.15.0 release, and won't be part of 2.0.0 release or nightly yet.

Cheers,

Yifei