orchestrator: Fix error catching in test
orchestrator: Fix error catching in test

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

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