Build serving against existing tensorflow build

[therealmitchconnors]

The io instructions for building serving automatically build tensorflow as a dependency for serving. Unfortunately, the docker files for serving are woefully inadequate for building tensorflow (more on that in another issue). Is there a way I can compile Serving against an existing build of tensorflow? Perhaps against binary in the the gcr.io/tensorflow/tensorflow:latest-devel container?

[therealmitchconnors]

Turns out this is already supported, though not terribly well-documented. Check out the last section of the setup docs for a good jumping off point.