Do not queue task for allocation unnecessarily
Do not queue task for allocation unnecessarily

Do not queue task for allocation unnecessarily when there are not
service allocations are pending or service allocations not needed.

Signed-off-by: Jana Radhakrishnan <045898bda7d4800fe4909a9831e702ab79e266be@docker.com>

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