Moving device model check to outside of Go code

[rvs]

This is something I've been meaning to do for quite some time (since the way device model check is currently implemented has been incorrect for quite some time). However, at the same time this is NOT a final form of this change.

At the same time -- since this is a bit of an emergency fix -- I apologize for rushing it through.

The salient points here are:

1. the check from Go code is gone for good -- it doesn't belong there (see below on where it belongs)
2. the script xen-info is a quick hack (and that is the part I need to apologize for) but it is going to get removed by the end of this week with a proper fix

So what IS a proper fix -- well, something similar to Kubernetes container liveness checks -- something that would apply equally to VM-based containers and baremetal containers alike. I'll start a thread on eve-tsc@ today to discuss a few strategies there.

[eriknordmark]

@rvs Don't understand why the old code did the sleep before the test/break. Do we need that 8 second delay?