Fix winsync agreements creation
    
    Due to recent addition of ID range support to DsInstance, the class
    could no longer be instantiated when realm_name was passed but
    ID range parameters were not. This condition broke winsync agreements
    creation in ipa-replica-manage.
    
    Make sure that ID range computation in DsInstance does not crash in
    this cases so that winsync replica can be created. Also convert --binddn
    option of ipa-replica-manage script to IPA native DN type so that
    setup_agreement does not crash.
    
    https://fedorahosted.org/freeipa/ticket/2987