453854: Clustersync: Support for "coalesce" functionality on
IClusterNotification 

same change as on develop (https://git.eclipse.org/r/#/c/37455/)

Change-Id: Ic2a6da8b956a722b6ea4a8a06fe93253024a200c
Task-Url: https://bugs.eclipse.org/bugs/show_bug.cgi?id=453854
Reviewed-on: https://git.eclipse.org/r/37493
Tested-by: Hudson CI
Reviewed-by: Christoph Schwank <christoph.schwank@bsiag.com>