Fix bug of accidentally deleting the build after compile

[ksaaskil]

This had the side-effect that the build was deleted after npm run compile. The bad news is that type-errors in tests are not detected but I think we can live with that for a while. To re-add, as far as I can see we could

1. Add a separate CI build step to compile tests. If running --clean after that, one would need to separately run npm run compile after the tests were cleaned.
2. Modify test compile so that it does not delete stuff from the build. I don't currently know enough of about the lerna+tsconfig but I think we can worry about it later.

FYI @mikesol @idantene