Refactor install-config

[stbenjam]

Based on 4.2 PR, which needs to get in first. Goes along with openshift-metal3/dev-scripts#578

Fixes #57

Some to-dos:

• Deal with image URL's, can we take them out of the install-config and use known adresses?
• Support creating the worker Ironic node objects (e.g. all the hosts we know about)
• Use the default profile in BMO when hardwareProfile is empty

[dhellmann]

/lgtm

This will make it much easier to add host registration, too.

[stbenjam]

Thanks, going to merge this so it's part of the 4.2 rebase. As discussed yesterday we can iterate on the issues identified above.