[rambo-296] Remaking conf file sections

[nixjdm]

(issue reference)
Fixes #296

Does this deserve / include a changlog entry? Included

Sample rambo.conf to work with this:

[configuration_management]                                                          
provision = false                                                                   
                                                                                    
[provider]                                                                          
provider = virtualbox                                                               
guest-os = ubuntu-1604                                                              
                                                                                    
[hardware]                                                                          
ram_size = 500 

This is a first attempt at a more granular section breakdown. It may be fine, or maybe we can come up with something better. For instance, I put machine_type in hardware, where I could also see it fitting into provider just as well. @smitty42 I think you might have an opinion on this.

[nixjdm]

Closing in favor of #336