Add Dockerfile
Add Dockerfile

Capable of running at least the sample pipeline. It's almost ready to
run the full publishing pipeline, but requires gapi-tools to be git
cloneable.

Change-Id: I99d145bd9ac41efb8c96f97e7520f39ef0fbbe55

shinfan/artman,googleapis/artman,ethanbao/artman,googleapis/artman,ethanbao/artman,googleapis/artman