Simplify re-encrypt logic

Want to introduce the ability to decrypt with an arbitrary key so we can convert from one v2_key to another. First step is to simplify the recrypt chain.

- separate auth_model_spec and auth_config_model_spec
- consolidate fix_auth#hardcode logic with recrypt logic


https://bugzilla.redhat.com/show_bug.cgi?id=1159009

/cc @jrafanie @Fryguy 
No, just noticed something and was wondering if you thought it made sense to extract/move stuff so we don't need to use subject.  I'm guilty as anyone of putting too many different contexts and setups in a spec... so if it makes sense to extract, do it as soon as it makes sense.