We used to install it only when Rust was configured, but for some
reason all builds now seem to be Rust builds. That's ok, so just
provide the necessary dependency.
We'd like to have some more structure to the tests, with smoke-tests
going first, followed by valgrind and normal tests running in
parallel. So to cut down on the copy-pasta we extract the scripts from
the yaml, into their own files from where they can be easily invoked.
