Remove private keys that are generated on install / first run #555
Description
Related to #550
We should remove secure-cookie-key and key.pem and friends from all of the instances when they are built
Alternatively, we could see if there is a nice way to stop the product from starting too... (setting an ARG, etc.)
### Tasks
- [ ] Add tests to ensure that secrets are not in images after build
- [ ] If necessary, stop products from starting on install by using an `ARG`
- [ ] If using `ARG`, make sure that licensing and directory permissions work on startup (and are tested)