fix: shutdown gracefully on TERM or INT signals

[ae-govau]

This allows server listen resources to be cleaned up appropriately.

What is the purpose of this change? What does it change?

• changes app to run within a context, and cleans up the server when the context is done.
• wraps several global variables up within a wrapper object, which makes the app easier to write tests for
• add a test helper function to start a server, then run client tests against it when it's ready
• add several tests to ensure the server is cleaned up properly.

Was the change discussed in an issue or in the forum before?

This is split from a different PR, PR #272.

Checklist

• [X] I have enabled maintainer edits for this PR
• [X] I have added tests for all changes in this PR
• [ ] I have added documentation for the changes (in the manual)
• [X] There's a new file in changelog/unreleased/ that describes the changes for our users (template here)
• [X] I have run gofmt on the code in all commits
• [X] All commit messages are formatted in the same style as the other commits in the repo
• [X] I'm done, this Pull Request is ready for review

[ae-govau]

Oh, I didn't notice that the tests are failing, the must be fixed before we can merge the PR.

Thanks, I'll look at today. Looks like it's the new test that I added which is failing. It's passing locally for me, so I'll have dig around to see if I can figure out why it's failing in the automation. I wonder if the test env doesn't allow a test to connect back to a server it started?

[ae-govau]

Tests are passing now.

[MichaelEischer]

Thanks!