OPENDJ-1929 Code cleanup

* ConfigFromDirContext.java
** readConfiguration(InitialLdapContext)
*** Reformat
*** Add final keyword
*** Rename local variables to make the code more readable
*** Extracted methods
**** readSchemaIfNeeded(InitialLdapContext, List)
**** readConfig(InitialLdapContext, Set<ConnectionHandlerDescriptor>, Set<BackendDescriptor>, Set<DN>, List<OpenDsException>)
**** readAdminConnector(RootCfgClient, List<OpenDsException>)
**** readConnectionHandlers(Set<ConnectionHandlerDescriptor>, RootCfgClient, List<OpenDsException>)
**** readBackendConfiguration(Set<BackendDescriptor>, RootCfgClient, List<OpenDsException>)
**** refreshLocalDBBackendConfig(Set<IndexDescriptor>, Set<VLVIndexDescriptor>, BackendCfgClient backend, List<OpenDsException>)
**** readIfReplicationIsSecure(RootCfgreadSyncProviderIfExists(final RootCfgClient root)Client, List<OpenDsException>)
**** readSyncProviderIfExists(RootCfgClient)
**** readReplicationConfig(Set<ConnectionHandlerDescriptor>, Set<BackendDescriptor>, ReplicationSynchronizationProviderCfgClient, boolean, List<OpenDsException>)
**** readAlternateBindDNs(Set<DN>, RootCfgClient, List<OpenDsException>)