Add migration-to-Linux case to switchtest
Should check that we come safely out of fault-related migrations from RT to Linux. Faults should be triggered both in userspace (see sigdebug test) as well as on userspace access from kernel space (see some tests in y2038). All that in tight loops in order to stress these paths more thoroughly.
Will need runtime silencing of the migration warning the cobalt core issues in debug configurations, or the kernel console will be flooded quickly.