Update ipmi test

[Jeff Lane ]

The current IPMI in-band test checks some arbitrary data to determine that you can communicate with the BMC in-band. This is to validate the facility that MAAS uses to auto=set user/password info and other things.

Also, one test in particular, the sensor data, isn't available in-band on some BMCs (ARM).

Need to change the test so that we look for things MAAS looks at instead, hence power and user data.