CEPH RPM repo key no longer available

The URL https://git.ceph.com/release.asc is no longer available (403 forbidden). Instead from https://docs.ceph.com/en/quincy/install/get-packages/ the correct way to install the CEPH repo key is

rpm --import 'https://download.ceph.com/keys/release.asc'

This is used in two places. I'll prepare a patch