Use cloud-init for reliable deployment of bridges rather than the provisioner hack

Right now the bridges are deployed with a couple of hacky SSHing in and running scripts steps. These often fail, especially when creating 10s of bridges simultaneously, and then your whole deployment needs to be redone. Rather, use the cloud-init resource in the template provider to provision the instances with user data.

This might be easy enough to do with the base Debian images which would make this more easily usable by other organisations wanting to run bridges, if not then this will require custom packer images.