Machine checks are flaky

[ajeddeloh]

Kola tests sometimes fail the machine check because systemd is still in the starting state.

Specifically sometimes this check times out while stilling in the "starting" state:
https://github.com/coreos/mantle/blob/master/platform/platform.go#L328

[arithx]

We can extend the timer (it's currently 300 seconds, 30 checks with one every 10 seconds) but at some interval it feels like there's a valid issue that the machine isn't finished starting.

[ajeddeloh]

I tried manholing in, but I kept getting weird terminal problems when I did (or it would fail on two machines at the same time and kola gets really confused when trying to manhole twice at the same time).