Gracefully handle bad sync updates

[rnpridgeon]

e2core may crash when receiving a corrupted update from se2. This may be because of a bad database migration, such was the case this week, or something else.

Rather than panicing e2core could mark these tenant overview updates as bad and either queue them for a subsequent retry for another time or ignore and log the bad update entirely.

In either case we want the execution environment to stay up even if that means serving stale data when faced with a bad update.