Change how hive test driver is enabled

[MegaRedHand]

Right now we use an env-var, but we should move to using a flag or subcommand, to be more explicit.

[IbrahimIjai]

Can I take sir, please?

[MegaRedHand]

This issue is about proposing an alternative to the current hive test driver, so it isn't a "good first issue". I recommend you look into other issues first. Let me know if you still want to work on this, though.