Fixed the broken tests in ReplicationServerTest.

ReplicationDbEnv.java:
Decoupled the call to start() from building the object + Made start() a public method.
Inlined the code from readDomainBaseDNGenerationIDRecords() and readServerIdDomainBaseDNRecords() into start() to avoid reading twice the DB on startup.
Extracted method openDatabase().

ReplicationServer.java:
In initialize(), called ReplicationDbEnv.start().