Support for unmanaged CPCs

[andy-maier]

The main review point I think would be how the unmanaged CPCs are surfaced by the cli:

This PR introduces a new command group with a single command:

zhmc unmanaged_cpc list

The original proposal in issue #98 was to add the list command to the console command group:

zhmc console list-unmanaged-cpcs

[coveralls]

Coverage: 31.679% (+0.05%) from 31.625% when pulling 0df62e4 on andy/add-unmanaged-cpcs into 259940b on master.

[simon-spinner]

That way we create a command group that doesn't correspond to an existing object on the WSAPI. I don't see it as an issue, because if the WSAPI would ever expose an operation for unmanaged CPCs, most probably it would introduce such an object as well.