Disable replication version plugin by default.
    
    The 389-ds replication plugin may not be installed on all platforms
    and our replication version plugin will cause 389-ds to not start
    if it is loaded and the replication plugin is not. So disable by
    default.
    
    When a replica is prepared we check for the replication plugin.
    If it exists we will enable the replication version plugin.
    
    Likewise on installation of a replica we check for existence of
    the repliation plugin and if it is there then we enable the version
    plugin before replication begins.
    
    ticket 918