test: Watchdog reset on lockups

[wkz]

To ensure that a system running Infix is always able to recover from any kind of lockup, we should add a test that creates a hard lockup that lasts longer than the watchdog timeout and verify that the system reboots.

Linux provides the test_lockup module for this purpose. For example, if the timeout is 60s, we can create a 65s hard lockup on all cores like this:

modprobe test_lockup all_cpus=1 disable_irq=1 time_secs=65

If, and only if, the watchdog has the capability to report the reset reason, the test should also verify that.

[wkz]

Fixed by #1321