Add options Sprint 14

Finish implementing what is covered in the Sprint 14 card:

https://trello.com/c/ChCOTSdf/216-avocado-virt-simplify-api-add-new-command-line-options

* Document the expectation/requirements/defaults of the image file that can be supplied by the user;
* Add options for username/password/hostname/etc, to be used together with a user supplied image when the user doesn't want the defaults;