Fix 2911 dsreplication pre/post-external initialisation fails to clear all the changelogs

Reminder: Inside the ReplicationDomain (plugin) the 'generation ID' and 'server State' both define the state of the server regarding the change occurred in the topology. The 'generation ID' defines the start point. The 'server 
State' defines an increment, and has a sense for the given generation ID.Thus the life cycle (loading/resetting) for the generation ID and state should be the same.

In particular at the end of an import, the generation ID is loaded or computed from the new data set.
The server Sate must be loaded or reinitialized the same way and this is not the case currently. That is what these changes fix.