Use Docker host network rather than bridging.

The default bridge network is known to be slow (1) and potentially
flaky (2). Switching to host networking is a desperate attempt to reduce
flaps in our nightly package builds.

(1) moby/moby#7857
(2) moby/moby#11407

Reviewed at https://reviews.apache.org/r/50716/

build-artifact.sh

@@ -34,6 +34,7 @@ run_build() {
 
   docker run \
     -e AURORA_VERSION=$AURORA_VERSION \
+    --net=host \
     -v "$(pwd)/specs:/specs:ro" \
     -v "$(realpath $RELEASE_TAR):/src.tar.gz:ro" \
     -t "$IMAGE_NAME" /build.sh