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r12b has been forever the default. Let's explicitly request that version
where we know we need it.

Note; there's other builds that still implicitly rely on that version
that don't use the buildjni flag. We don't really have a good way of
finding those, except manually.

- use apt-get instead of apt
- do apt-get update || apt-get update before apt-get install
- use apt install -y