This PR adds a job mutator which injects constraints on the job taskgroups
that make use of bridge networking. Creating a bridge network makes use of the
CNI plugins: bridge, firewall, host-local, loopback, and portmap. Starting
with Nomad 1.5 these plugins are fingerprinted on each node, and as such we
can ensure jobs are correctly scheduled only on nodes where they are available,
when needed.
