Ensure drivers loaded before failing

so that deprecated are known
PLAT-132

@e0d plz test: this should fix your problem
any(@doctoryes @mulby @cpennington) plz review

Did red, green TDD
unsetting the cache doesn't remove the `deprecated_fallback` attr from the class. Removing the attr doesn't work b/c python doesn't reload the module. I'll need to look into manually reloading / unloading modules