maas auto-creates interface name for docker bridge on controller, which breaks bind

[Tessa]

Hi MAAS friends,

We just ran into a new weird issue. After upgrading an older controller to v3.1, it generated some new interface entries from the controller's current config, including one named "docker_gwbridge". in then tries to turn this into a DNS name, and this breaks bind completely, since you can't have underscores in dns names. because the system is the maas controller, I don't seem to be able to remove the interface from maas, using either the webui or the cli, nor can I rename it. ideally, MAAS should just sanitize all auto-generated DNS names so that this can never happen, but regardless, I'd be happy with a workaround that stops it from trying to generate entries for docker bridges.

thanks!