updater: Avoid getting tasks stuck in READY
updater: Avoid getting tasks stuck in READY

The updater would incorrectly skip moving the new task to RUNNING if it
was replacing a task that had a desired state other than RUNNING. Fix
this to always move the new task to RUNNING.

This also fixes a case where the updater might move a preexisting task
to RUNNING before the running task in the slot had been shut down.

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

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