bug 895771 - fix jenkins tests

Subtree merging socorro-crashstats went smoothly for the repository, but it messed up all our build infrastructure. An earlier PR attempted to fix this and after 24 hours I was spinning yak wool into yarn and Jenkins remained broken.

The ambition is to:
- [ ] separate tests from building the artifact
- [ ] separate socorro and webapp-django commands
- [ ] have leeroy run both socorro and socorro-crashstats tests
- [ ] retain independent jobs to prevent ops from having to change deployment infra with no warning

Here I'm starting over with better local testing before anything gets pushed up. This will track a fresh attempt at the problem.