fix bwscanner network

The bwscanner network was previously unused, and broken. It was added for the bwscanner CI, but that later started patching its own version of the network script and corresponding templates into chutney. The latter broke with recent changes to chutney: tpo/network-health/sbws#40225 (comment 3136078)

This fixes a couple issues with the network so that it bootstraps correctly, with the intent that the bwscanner CI can start using it instead of trying to patch in its own version.