Misc fixes may21

[ripleymj]

Just a few cleanups discovered in playing with the codebase lately.

1. Eclipse Checkstyle has moved the repository, so update that URL
2. The stu-home shortcut uses Cinnamon Nemo and doesn't work with Ubuntu, so make that a mint-only task. Ubuntu shortcuts also seem to require world-exec and gio set file.desktop "metadata::trusted" yes to run
3. Ubuntu 21.04 packer aborts without the apt "-y" flag, which we use elsewhere and most examples seem to show. I'm not sure how this was working before, but I think noninteractive mode is meant to suppress package prompts
4. The Ubuntu ISO checker is running on forks, which would likely cause diverging commits on the main branch

[laurelmay]

Thanks for catching these. Definitely have no idea how apt was ever working before. We definitely shouldn't have been expecting it to. Good stuff.

[laurelmay]

Looks like ansible-lint is now grumpy about some unrelated things (but just grumpy; not failing) with ignore_errors. We can track this separately.