actively replace 'unknown' Marathon tasks

[Rob-Johnson]

Marathon seems to lose the Healthcheck actor for a given task occasionally, leaving it in an 'unknown' state. Let's actively go after these in the bounce and replace them where we can

[Rob-Johnson]

I think this could be a good one to go after @matthewbentley . we should chat to @jvperrin to see if the issues we've seen lately with 'unknown' tasks were isolated to norcal-prod (and marathon 1.1)