Add get_fields method to orm.Entity
Merge pull request #934 from Ichimonji10/entities

Add class `Model` to module `robottelo.entities`
Merge pull request #925 from elyezer/orm-get-fields

Add get_fields method to orm.Entity
Add new module `robottelo.factories`

Do not include any useful code in this module. Instead, simply write out a
docstring.

Make the API docs include this new module.
Add minimal content to module robottelo.factories

Create the following classes:

* Factory
* HostFactory (inherits from Factory)
* ModelFactory (inherits from Factory)

Implement the following methods on `Factory`:

* `__init__`
* `attributes`

The new factories can be used for quickly building new entities on a Foreman
server.
Add test for method _get_protected_fields

Tested method is in module `robottelo.factories`.