Reproducible random

[jayvdb]

In order to have random tested dependencies (see #187), the moban approach would be to create requirements-random.txt.

To do that, moban needs a stable randomiser. Re-running moban should produce the same output.

The easiest approach I can think of is to use the top git commit as the randomiser salt.

And if git isnt present, a hash of all of the templates, or something similar. Or potentially each target has a different salt, being the hash of its template.