Fix delegate_to expression in download tasks
Fix delegate_to expression in download tasks

"else omit" is causing problems in this expression. Replacing
it with more strict "inventory_hostname" fixes the issue and
handles `download_run_once` as expected.

Closes issue #514

hatch-k8s/kargo,kubernetes-incubator/kubespray,Atoms/kubespray,galthaus/setup-kubernetes,sgm-media/kargo,Atoms/kubespray,Atoms/kubespray,ayaz/kubespray,sgm-media/kargo,jcsirot/kubespray,rogerwelin/kargo,Abdelsalam-Abbas/kubespray_fork,Lendico/kargo,kubespray/kargo,kubespray/kargo,galthaus/setup-kubernetes,ayaz/kubespray,insequent/kargo,VincentS/kargo,jcsirot/kubespray,kubernetes-incubator/kargo,kubernetes-incubator/kargo,kubernetes-sigs/kubespray,VincentS/kargo,Atoms/kubespray,kubernetes-sigs/kubespray,Abdelsalam-Abbas/kubespray_fork,rogerwelin/kargo,hatch-k8s/kargo,kubernetes-incubator/kubespray,Lendico/kargo,kubernetes-sigs/kubespray,kubernetes-sigs/kubespray,insequent/kargo