destroy_test: add a destroy test for non-existent units
destroy_test: add a destroy test for non-existent units

giantswarm/fleet,giantswarm/fleet,dongsupark/fleet,improbable-io/fleet,jonboulle/fleet,dongsupark/fleet,coreos/fleet,jonboulle/fleet,dalbani/fleet,coreos/fleet,endocode/fleet,improbable-io/fleet,endocode/fleet,jonboulle/fleet,improbable-io/fleet,endocode/fleet,dongsupark/fleet,dalbani/fleet,dalbani/fleet,giantswarm/fleet,coreos/fleet