This PR enables users of Nomad < 0.12 to upgrade to Nomad 0.12
and beyond. Nomad 0.12 introduced a network fingerprinter for
bridge networks, which is a contstraint checked for if bridge
network is being used. If users upgrade servers first as is
recommended, suddenly no clients running older versions of Nomad
will satisfy the bridge network resource constraint. Instead,
this change only enforces the constraint if the Nomad client
version is also >= 0.12.
Closes#8423