extend consoleChecks to testiso tests

[dustymabe]

We have a long list of console checks compiled in https://github.com/coreos/coreos-assembler/blob/429241d0a487b4f0a7e063c2731d49a5b432bee2/mantle/kola/harness.go#L126-L201

But we don't apply any of these checks to our testiso tests. It might be worth investigating how we can also apply these checks there as well.