OPENDJ-1116 Introduce abstraction for the changelog DB

Removed avoidable references to replicationServerDomain.getReplicationServer().
Code cleanups:
- collapsed if statements
- applied early exits
- Replaced useless use of StringBulders with string concatenations
- Removed useless parentheses


*ServerHandler.java:
Replaced calls to this.replicationServerDomain.getReplicationServer() with directly using this.replicationServer .

DataServerHandler.java:
Inlined local variables.
Removed useless catch.

ECLServerHandler.java:
Extracted method releaseIterator().

LightweightServerHandler.java:
Extracted method getLocalRSMonitorInstanceName().

ReplicationServerHandler.java
In isRemoteLDAPServer(), renamed parameter.


MessageHandler.java:
Extracted methods collectAllIteratorsWithChanges(), addIteratorIfNotEmpty(), releaseAllIterators().

ReplicationServerDomain.java
Renamed replicationServer to localReplicationServer.
In put(), renamed id to serverId + extracted method publishMessage().
In getChangelogIterator(), renamed parameter.
Extracted methods replyWithMonitorMsg(), replyWithUnroutableMsgType(), forwardMsgToAllServers(), replyWithUnreachablePeerMsg() from process().
Renamed stopDbHandlers() to shutdownDbHandlers().
Extracted isServerConnected() from getEligibleCN().



DbHandler.java, JEReplicationIterator.java:
Renamed parameter.