global orchestrator: reconcile more than one service at a time
global orchestrator: reconcile more than one service at a time

This can avoid doing extra raft writes, and reading extra data from the
store.

Signed-off-by: Aaron Lehmann <8ecfc6017a87905413dcd7d63696a2a4c351b604@docker.com>

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