SwarmKit: updateService does not return proper gRPC errors for some errors. Also, no error is returned if a service cannot be found.
SwarmKit: updateService does not return proper gRPC errors for some errors. Also, no error is returned if a service cannot be found.

Signed-off-by: Daniel Zhang <de92742b6296b43ec0adf7cdc363523e395e8ab5@gmail.com>

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