Build scenario to test behavior with adversarial tasks

[markstory]

It is possible for tasks to present adversarial behaviour. This can take the form of workers that consistently exceed their processing deadlines, or never update a task's status.

• Create a misbehaving worker that exceeds processing deadlines and never updates task status.
• Use this worker to handle a task backlog of a few thousand tasks

Questions to answer:

• Does taskbroker get 'stuck' as long running tasks accumulate in sqlite?
• Do these missed task updates show up in our metrics or logs?