testrunner: pass through /dev/kvm to containers

For reasons I haven't dug in too much, `oci-kvm-hook` doesn't work on
F25 (though it does on F27). Howver, the nodes are currently stuck at
F25 because of severe issues with `docker cp` in newer version
(rhbz#1489505). So let's just explicitly pass /dev/kvm into the
container, which is all `oci-kvm-hook` is trying to do anyway. I've
verified this works.

This will unblock ostreedev/ostree#1462.

papr/testrunner

@@ -74,6 +74,7 @@ provision_container() {
     fi
 
     sudo docker run --name $name -d \
+        --device /dev/kvm \
         --cidfile $state/cid \
         "$image" sleep infinity