Add Environment v2 Builder (#298)

Build server and client for environments.

This build server will run inside environment builders and invoke environment-specific scripts for doing builds. It provides a uniform language-independent API for builds to the fission build manager.

The change also includes an implementation of a builder for Python -- this "builder" acts on requirements.txt and runs `pip install` to collect all function deps.

builder/cmd/Dockerfile

@@ -0,0 +1,5 @@
+FROM alpine:3.4
+
+ADD builder /
+
+EXPOSE 8000