We're going to write a helper binary for this in Go, because:

- The currently maintained driver package supports mongo versions back
  to 2.6 (what we're using), which is not true for most other languages.
- We already have go in our toolchain for boringssl's test suite.
- The build is unlikely to break due to bitrot re: Go's toolchain.
- The generated binary is static, so all else fails we can just bundle
  the executable, though I don't anticipate that.
- I will be much more productive than in something else.

I'm getting a permissions error trying to just run this from my local
dev directory; need to figure out what's going on.

We're successfully listing the collections.

Also make the flag an integer instead of a string.