[ceph] Use the Mirantis repo for patched Ceph packages
Squid 19.2.1 contains an RGW bug that causes all of the ACL-based Tempest tests to fail. This pulls Ceph packages from the Mirantis repo instead of download.ceph.com. The Mirantis build includes a patch for this issue. Change-Id: Iaa50a7dc7928240579e221b7b35e736dd790c85d