We call dispatcher scripts for both NM-initiated activations and for activations that NM merely observes. For many dispatcher scripts, this is the right thing, but potentially not for all of them. So this branch adds a CONNECTION_EXTERNAL=1 variable to the dispatcher environment when dispatching events on a generated-assumed connection.

(Note that this is built on top of danw/policy-based-routing-rh1160013. I was going to add a check for !$CONNECTION_EXTERNAL to 10-ifcfg-rh-routes.sh, but realized it's not actually needed since it's effectively covered by the $CONNECTION_FILENAME check.)