Add plugingetter to swarm node config.
Add plugingetter to swarm node config.

This is necessary for swarmkit to support cluster wide plugins, such as
globally scoped network plugins.

Signed-off-by: Anusha Ragunathan <ab61560b6c027d679611acf9b4b553fb22d61c05@docker.com>

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