Bug#887382: Release clojure1.9 on the masses

[intrigeri]

Elana Hashman:
> This is ready to migrate down to testing now.

Great news!

> I was waiting for two things:

> - ensure 1.9 and 1.8 can be simultaneously installed (required fixing
>   the alternatives logic)
> - piuparts tests actually passed

> These are both fixed so let us loose 1.9 on the world of testing
> users.

Thanks a lot for the clarification!