.automated_script.sh: add proper HTTP status checking

When a download attempt fails with an HTTP error, the body of the failed request will be written to the output file with a 0 exit status, causing the execution of an error message as a script.

This issue is resolved by adding the --fail option to curl.

configs/releng/airootfs/root/.automated_script.sh

@@ -23,7 +23,7 @@ automated_script() {
                 sleep 1
             done
             printf '%s: downloading %s\n' "$0" "${script}"
-            curl "${script}" --location --retry-connrefused --retry 10 -s -o /tmp/startup_script
+            curl "${script}" --location --retry-connrefused --retry 10 --fail -s -o /tmp/startup_script
             rt=$?
         else
             cp "${script}" /tmp/startup_script