Code review comment for lp:~rvb/maas/add-power-params-doc

I don't think we should be documenting this like this, other than some
examples perhaps.

This is because clusters can and will have varying power types available
- it's not a heterogeneous environment, especially during staged cluster
upgrades.

What I think we should do is implement an API function that returns
available power types and each one's parameters based on the cluster and
encourage API users to derive from that when editing/adding nodes.