On the new versions of RHEL, the network service isn't enabled by
default because this mechanism became legacy.
However, our os-net-config doesn't use the new network manager, so we
still rely on on the network service to manage things like the virtual
bridges on the Undercloud and the Overcloud.
Change-Id: Iceeeef8535738093be2438abd9deec99f5d61c1b
Closes-Bug: #1823353