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 
Want to test AuthConfigModel.
But don't want to mixin and redefine the models. So I just leverage the existing one.

You want to split these up into each model that we are testing?