Collect missing events

[webignition]

job/ended event is received with sequence_number 10. Only 7 events have been received for the relevant job. From these we can figure out the sequence numbers of the missing events and request these from the worker.

Will need:

• background jobs to handle collection
• maximum retry limit per missing event
• time limit for whole process
• new collecting_events job status

[webignition]

Event collection might also be requested externally, most likely by the job coordinator.

The job coordinator has the ability to determine when the results state is sufficiently out of sync with the worker state and can then request that the results service retrieve events from the worker.