Read lesson requirements directly from the lesson repositories

[wking]

This is a long-term goal expanding on @pbanaszkiewicz's suggestion.

On Wed, Mar 11, 2015 at 03:08:15PM -0700, Piotr Banaszkiewicz wrote:

1. Maybe add workshop-template/requirements.txt (not necessarily a
   Python dependencies file) that's read by installation testing script
   and adjusts CHECKS entries accordingly?

That would work, but we are currently recommending folks install
Anaconda (swcarpentry/DEPRECATED-bc#724), so we don't have package-level resolution on what a workshop
needs. If the workshop instructors need to tweak a file to
list their requirements, I think it might as well be the
installation-test script itself. Once the lesson and workshop-template
repositories mature a bit, we could have:

a. The per-workshop repository maintain a list of the lessons it's
teaching (with URLs for the lesson repositories).
b. The per-lesson repositories listing their requirements for the
installation-test script.

Then you could:

$ python swc-installation-test-2.py --lessons https://efran.github.io/2015-04-09-UW/lessons.txt

and have the installation-test script lookup the listed lessons, fetch
their requirements, and iterate through them to make sure all the
requirements were satisfied.