test: verify failure-config and RMA mode

[troglobit]

Usually the system boots up nicely with startup-config (if that doesn't exist it creates one from factory-config). But if Infix fails to load startup it should fail-over to failure-config and give login prompt. If for some reason that too fails, then we're in RMA mode.

In all these modes the getty should start (but only getty, no other login services!) so that developer builds with a root account can log in and diagnose the system.

These aspects of the boot need a regression test to prevent late release cycle stress when it turns out these things don't work.