(#21069) refresh the cache of launchd plists on a miss

[djmitche]

This refactors jobsearch a little and makes it refresh the cache in the case where it cannot find a label. This should fix the (relatively common!) case where a launchd plist is added with a file resource, then enabled with a service resource.

[puppetcla]

CLA signed by all contributors.

[adrienthebo]

For expectations on blocks, expect { }.to is preferred over lambda { }.should

[adrienthebo]

Thank you very much for this contribution! I had a couple of small comments on style, but this looks very good!

[djmitche]

I was off for a long weekend, but I'll fix this up this week.

[djmitche]

Updated. Note that this conflicts with another update made since this was branched. I can rebase and file a new PR, but the conflict should be fairly simple to resolve on mrege.

[adrienthebo]

You can just rebase this pull request and then force push to the branch that this was filed against, and the pull request well be updated in place (if that helps).

[djmitche]

This ended up pretty substantially revised as far as tests go, so please do have another look.

[adrienthebo]

summary: merged into master in 3ca75a6; this should be released in 3.4.0. Thanks again for the contribution!