Add -m flag for tests

[clrcrl]

Tried to use this flag today but it wasn't there

[drewbanin]

dang, good catch. Merge it when the tests pass

[beckjake]

Great PR!

In general, why are tests not part of the same subcommand list as compile/run? Just because of --non-destructive and --full-refresh? If that's the case, shouldn't docs generate behave like tests?

[drewbanin]

@beckjake yeah - i think test probably belongs in that list more than docs does, right? This is kind of fuzzy, but I think we included the docs subparser in that list because dbt docs generate invokes compilation, and full-refresh/non-destructive mutate the resulting compiled SQL.

Regardless, i think test should get --models, --exclude and --threads from the same place the rest of the subparsers do.

[drewbanin]

let's merge this for grace-kelly and then cleanup main.py more broadly in a future release