check_disk: show troubled partition in verbose mode

I'm submitting a small patch to check_disk that will show which partitions are
actually causing the error state. This helps the human operator to quickly
identify the exact issue. I made it so a single -v flag is required so it
doesn't harm legacy code that may be parsing the original style of output.

Thanks to Jason Benguerel.
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Closes #984
Closes #1182
Adding Jason Benguerel