Update the Ceph repo key URLs
Summary
Replaces the present Ceph public key URL, which no longer resolves, with the URL given in the documentation at https://docs.ceph.com/en/pacific/install/install-storage-cluster/#installing-with-rpm .
This branch does not replace wget
with rpm --import
for the purpose of importing the key, as it allows us to leave the gpgkey file specification in https://docs.ceph.com/en/pacific/install/install-storage-cluster/#installing-with-rpm
as is.
Requires manual tests in pre-production
No, any problems should get picked up by CI.
References
Closes #219 (closed)