When the NIC configs were unified under a single role.role.j2.yaml,
the bridge name for Ceph roles was changed from "br-storage" or
"br-bond" to "br-ex". This breaks upgrades which used the original
NIC config templates. This change reverts those valuse when
rendering the NIC config templates for CephStorage roles.
Closes-Bug: #1766748
Change-Id: I68b6e674d6aa86aa7d60efa3eb7b3cb874171e63