ref(builder): replace python with bash

Debugging the builder script when it fails is really difficult in
python. You have to import a bunch of libraries, pipe stderr on some
commands to stdout, inspect the return codes and the error returned...
In short, it's quite difficult to debug. Refactoring to bash allows us
to debug the script quite easily by setting the -x option for bash
scripts and we have instant debugging.

This refactor also removes the "remote:" prefix from most of the
output, which is another huge plus.
style(builder): styling nitpicks
fix(builder): exit if response is bad
fix(builder): suppress stderr

We don't need to know that parsing the object failed, as we're going
to print the controller response shortly after. These errors do not
provide anything useful. It's the controller response that we're
interested in.
fix(builder): pipe envvars to temp file
fix(builder): do not add build option if empty
fix(builder): compiled slug is no longer a tarball
Merge pull request #1859 from bacongobbler/builder-refactor

ref(builder): replace python with bash