Sometimes a paladin slave doesn't start on time because the dedicated buildslave is down and there aren't enough floating buildslaves.

We'd like to alert on this so the deputy can go reclaim buildslaves.

Since the paladin-master now waits for all important build slaves to start off (and we retry if they fail soon enough, iiuc), it should be possible to send  monarch metric with (#of important build slaves that buildbucket failed to schedule entirely).
We can then alert on this metric.

nxia@: Is it reasonable to add such a metric?