use the drone cli to check that the starlark is well-formed,
and to try to run a build.
Useful for sanity checking a pending CI commit.
Slim down the deps very slight on ubuntu systems.
The drone plugin does stuff very strangely and is incompatible
with our approach.
Do it ourselves (with blackjack and ...), so that we can avoid
cloning and bloating the repo.
drone
Wez Furlong