devref: added more details on rolling upgrade for notifications
devref: added more details on rolling upgrade for notifications

Change-Id: I585c8792d63d79bb88a6c946863b49952bd6140f

eayunstack/neutron,wolverineav/neutron,dims/neutron,huntxu/neutron,cloudbase/neutron,wolverineav/neutron,openstack/neutron,igor-toga/local-snat,bigswitch/neutron,sebrandon1/neutron,bigswitch/neutron,noironetworks/neutron,MaximNevrov/neutron,igor-toga/local-snat,mahak/neutron,openstack/neutron,noironetworks/neutron,openstack/neutron,mahak/neutron,sebrandon1/neutron,klmitch/neutron,eayunstack/neutron,dims/neutron,huntxu/neutron,cloudbase/neutron,mahak/neutron,klmitch/neutron,MaximNevrov/neutron