orchestrator: Delete tasks of non-existing services at start.
orchestrator: Delete tasks of non-existing services at start.

Starting the orchestrator would set tasks of deleted services to
DesiredState=DEAD.

This is a different behavior of what we do live, which is to delete the
task.

Signed-off-by: Andrea Luzzardi <442ffe3ffbfd024afcf0b7f8b108d05bca3aae43@gmail.com>

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