generic/centos7: network auto_config disable isn't properly handled

[poige]

Have :auto_config => false, per an interface in Vagrantfile and realise that in despite of that NetworkManager™ is happily trying to bring the interface up:

eth2: connecting (getting IP configuration) to Wired connection 1

Another q-n would be why it's NetworkManager there after all but if it's there it should be aware of the option.