Make deprecation of clustered option work and document HQ221038
Merge pull request #980 from ecki/topic-deprecate-clustered-param

Make deprecation of clustered option work and document HQ221038
checking existing paging store before putting a new one into the map.

This avoids the same paging store being started twice.
fix bug: https://bugzilla.redhat.com/show_bug.cgi?id=900899