OPENDJ-1441 (CR-4037) Persistent searches on external changelog do not return changes for new replicas and new domains

Fixed a problem introduced in r10918.

In getExistingOrNewDomainMap(DN) method, the MultimasterReplication.isECLEnabledDomain() method is called.
However, this method blocks forever at replication startup because MultimasterReplication state is equals to STARTING
and is only set to RUNNING in code that occurs after in the same thread.

Code sequence is :
1. SynchronizationProviderConfigManager calls MultimasterReplication.initializeSynchronizationProvider()
   try to call MultimasterReplication.isECLEnabledDomain() but MultimasterReplication state is equals 
   to STARTING so it waits indefinitely on a state change
2. SynchronizationProviderConfigManager calls DirectoryServer.registerSynchronizationProvider(provider)
   MultimasterReplication state is set to RUNNING

Add a check on registeredMultiDomainCursors to ensure that isECLEnabledDomain() is not called when 
the replication server is starting (as no cursors can be created yet).