Only allow retiring of packages in certain branches

[tyll]

Looking at

pdc-updater/pdcupdater/handlers/retirement.py

Line 33 in b07055e

def handle(self, pdc, msg):

it appears to me that pdc-updater does not ensure that packages are only retired in certain branches, these should be the EPEL branches, the Rawhide branch and the current branch for Branched until the final freeze deadline. Not sure how it is planned for custom branches. It should not be possible to retire pkgs in f25/f26.