OPENDJ-1606 (CR-4909) ConcurrentModificationException while performing modify operation against two replicated DS


Fixed ConcurrentModificationException.
I suspect the NoSuchElementException is thrown by the desugared foreach loop on an ArrayList.

JEChangelogDB.java, FileChangelogDB.java:
FOr the fields registeredDomainCursors and replicaCursors, replaced the use of ArrayList + synchronized keywords with using ConcurrentSkipListMap + CopyOnWriteArrayList to ensure thread safe access/modifications of these MultiMaps.
Created putInMultiMap().
Aligned code between the 2 implementations.