OAK-1932: TarMK compaction can create mixed segments

Avoid triggering revision cleanup at each new tar file.
Instead it gets triggered after compaction.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1608783 13f79535-47bb-0310-9956-ffa450edef68
OAK-1863: Generic operation tasks should be able to return specific results
Parametrise ManagementOperation on the return type of the passed task

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1608797 13f79535-47bb-0310-9956-ffa450edef68