Add the ifcfg-* template for 'network.managed' to work on RHEL7

Exact same as RHEL6 configuration, but the [official docs](https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Networking_Guide/sec-Using_the_Command_Line_Interface.html#sec-Configuring_a_Network_Interface_Using_ifcg_Files) show no changes. For my production environment, I've got a state which literally copies this file out so that `network.managed` works