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.


- separate auth_model_spec and auth_config_model_spec
- consolidate fix_auth#hardcode logic with rencrypt logic
- encrypt_version_{1,2}(str) -> encrypt_version(str, #, key)
- decrypt_version_{0,1,2}(str) -> key.decrypt64(str)
  (it was a partial implementation of decrypt)

https://bugzilla.redhat.com/show_bug.cgi?id=1159009

/cc @jrafanie @Fryguy 
@matthewd `super` is ActiveRecord::Base - it is the class hierarchy with no regards to the modules. Didn't matter if I removed concerns and used include - it doesn't modify the class hierarchy chain.

The only way I found to do this was to fetch the method from the module and call directly:

```ruby
FixAuth::AuthModel::ClassMethods.instance_method(:recrypt).bind(self)
```