Re-model the job auth

We have decided to rename the 'password' auth to 'secrets' on the
zuulv3 spec.
The idea is that we will both encrypt the user and password using
PKCS1, also allowing to have more than one secrets.
This change modifies the model to meet new spec requirements.

Change-Id: Ief78ac27732f30b17d7995a3e2032e33e7979ca9
2 files changed