expand ceph-osd node count error message

Clarify to the operator what needs to be done to resolve the problem
reported in the error message that is generated by post-deployment
checks when the number of ceph-osd nodes is less than the configured
Ceph data replication factor.

Change-Id: I8d341842bd8e6d879703c7e39a89a79c426cbbde
Merge "expand ceph-osd node count error message"