Updated openstack/openstack
Project: openstack/ceilometer  5c938c1f2b82b6876d6cd5980bbcdb660293a544

Improve manual.rst file

Adds description and instruction in manuals.rst file at MongoDB section for
case when replica set mode is required.

Change-Id: I346ae134776766533cc9b72f628f2c85f2ce6d1a