Use HTTP status code names, not numbers
Move function into module robottelo.api.utils

Function `status_code_error` is useful in numerious different tests. Promote it
from being a private helper function to a public function. Adjust other code to
deal with the change
Add tests for "domains/" path.
Add support for field default values and choices

If a field specifies that it has a default value or offers some set of choices,
then its get_value() method should respect that statement. Make fields do so,
and add tests to ensure that this is the case.
Add tests for "repositories/" paths.

As part of this effort, also fix up the Product entity's fields, make
URLField.get_value return a better value, and improve the error handling of
class Factory.