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 
@kbrock I can't tell how you're calling recrypt but you can do ancestors on the object (self maybe?) to see the ancestry to know what module has the recrypt method that is coming before yours.  Module#prepend, may be the answer but you have to look at the ancestry to know.