Change test timeouts to be in realtime

[TrentHouliston]

The current tests use on for timing out tests.
This doesn't work if you manipulate the clock as the watchdog may never fire.

This changes it to just waiting for a specific amount of real time before ending the test.

Also makes the following other changes

• Makes the amount of time to wait a constuctor arugment rather than a template argument
• Makes a Fail struct that can be emitted to fail the test with a message (used by timeout)
• Adds a force option to powerplant shutdown to make it remove all queued tasks