I was having the same issue.
In the yaml files describing the Replication Controllers, I was using keyring: in the volume section:
keyring: "ceph.client.admin.keyring"
After I generated a Ceph secret and changed the yaml files to use secretRef:
secretRef:
name: "ceph-secret"
Kubernetes was able to map and mount the Ceph volumes and the pods began to start normally. I don't know why using keyring: doesn't work in this case.