Support all Fog OpenStack options

[BobbyRyterski]

This loads all the openstack options directly from Fog and calculates the optional settings so we don't have to chase OpenStack / Fog changes.

With fog 1.33.0, #optional_server_settings returns:

[
  :openstack_auth_token, :openstack_management_url, :openstack_service_type, 
  :openstack_service_name, :openstack_tenant, :openstack_tenant_id, 
  :openstack_identity_endpoint, :openstack_region, :openstack_endpoint_type, 
  :openstack_project_name, :openstack_project_id, :openstack_project_domain, 
  :openstack_user_domain, :openstack_domain_name, :openstack_project_domain_id, 
  :openstack_user_domain_id, :openstack_domain_id
]

I originally intended to only add the OpenStack identity v3 options, but I think this ended up as a neater solution.

[BobbyRyterski]

Not the best test, but too much else seemed like reimplementing the function.

[jjasghar]

Can you add something to the README.md about/possible options? Having support for this is awesome, but we need some words saying we have support too 😸

[BobbyRyterski]

How's this sound?

I would've liked to have a link to a definitive list of options, but I couldn't find one in the docs. We could link to the code, I guess.

[jjasghar]

Yeah this is fine. People looking for the options'll know what to look for. Thanks!

[jjasghar]

Cool, now I'd like another 👍 from someone other than you or me, and i can add this to the next release.

[david-crowder]

Not sure if this counts (@BobbyRyterski is a coworker), but I have tested this branch and everything works as expected. So while not an impartial 👍, I do support this change 😃

[BobbyRyterski]

Sounds good, @jjasghar. I'll rebase now so it'll be all nice and neat.