dispatcher: send managers list before disconnect
dispatcher: send managers list before disconnect

Signed-off-by: Alexander Morozov <2043cda4df124b840b98ee1c4307c199042efdf7@gmail.com>

RenaudWasTaken/swarmkit,jlhawn/swarmkit,cheyang/swarmkit,allencloud/swarmkit,docker/swarmkit,AliyunContainerService/swarmkit,yongtang/swarmkit,Noyan759/swarmkit,aaronlehmann/swarmkit,jlhawn/swarmkit,AliyunContainerService/swarmkit,dperny/swarmkit-1,runshenzhu/swarmkit,diogomonica/swarmkit,yp-engineering/swarmkit,diogomonica/swarmkit,elifa/swarmkit,yp-engineering/swarmkit,deljuven/swarmkit,aaronlehmann/swarmkit,allencloud/swarmkit,runshenzhu/swarmkit,fate-grand-order/swarmkit,alyyousuf7/swarmkit,cezarsa/swarmkit,sungwonh/swarmkit,vasil-yordanov/swarmkit,elifa/swarmkit,sungwonh/swarmkit,alyyousuf7/swarmkit,docker/swarmkit,dperny/swarmkit-1,RenaudWasTaken/swarmkit,deljuven/swarmkit,Noyan759/swarmkit,fate-grand-order/swarmkit,cheyang/swarmkit,yongtang/swarmkit,vasil-yordanov/swarmkit,cezarsa/swarmkit