Build Cop: add test failure log to issues

[ace-n]

As title. 🙂

If this log is not included, it can cause spurious (and practically un-debuggable! 😱) failures like this one if the log cannot be retrieved in some other way.

[tbpg]

Thanks! One concern to keep in mind is that failure logs can be long. So, we might want to wrap the log in a collapsible element. Emails would still be long, but I think that's OK.

[tbpg]

Thank you for the feature request! Feel free to file another issue if there is anything else we can improve (or this doesn't work as expected). :)