Rewrite bug selection logic

[AndrewFasano]

competition_bugs_and_non_bugs in scripts/competition.py:66 is terrible and needs a rewrite. The uninjected_random_... functions in scripts/lava.py should probably be updated as well in the process.

As the name suggestions, competition_bugs_and_non_bugs, is used during competitions, but the uninjected_random functions are used more commonly and the competition is the most complex consumer of those functions, so we should probably start the rewrite there.