Update web dockerfile to use dev deps when building prod assets

[klingerf]

This branch fixes a master branch CI failure that was introduced in #976. Specifically, the bin/docker-build-web script is failing due to docker not being able to find dev dependencies, such as "babel-loader", when running NODE_ENV=production yarn webpack.

The issue arises from these stages in the Dockerfile:

# node dependencies
RUN $ROOT/bin/web setup --pure-lockfile

# frontend assets
# set the env to production *after* yarn has done an install, to make sure all
# libraries required for building are included.
ENV NODE_ENV production
RUN $ROOT/bin/web build

Calling web setup the first time effectively runs NODE_ENV=development yarn, which installs the development dependencies that we need. Unfortunately, calling web build also calls web setup, and that causes us to re-run the setup with NODE_ENV=production yarn, which removes the development dependencies that were previously installed.

A different fix for this would be to modify web build to stop calling setup, and require that folks run the setup command explicitly, as needed. Since setup only really needs to be called when package.json changes, that would also speed up steady-state development. @grampelberg thoughts?

[klingerf]

A different fix for this would be to modify web build to stop calling setup, and require that folks run the setup command explicitly, as needed.

I have this change ready to go and am going to push it as a separate commit to this branch.

[siggy]

I don't have the full context on this change and #976, but can confirm that bin/docker-build, bin/web, and bin/web run work on this branch.

[grampelberg]

Gah, totally my bad =/ Sorry about that.