Cleanup of code from PR reviews.

- Some cleanup in the code where action_url is being set, moved that into its own method.
- More cleanup in the area where attributes are being set for MiqAeField. Changed name of the form field for substitute column so looping over form fields in controller to set MiqAeField attributes gets easier.
- Updated spec test to use miq_ae_domain_enabled and miq_ae_domain_disabled factories.
- Fixed an issue found with Domain delete during testing.

Issue #2045