[adc] add broken node metrics
Add a broken-node metric
(counter) VMs that are determined to be "broken nodes"
Add a label to separate VMs marked as broken before the first container is started on them (likely boot problem) and after (likely container related problem).
Note that we already have a boot outcome metric. Make sure that we increment the broken node counter ("before first container" label) when we have a boot outcome == failed, though not in the timeout case.