networking.dhcp fact is blank on RedHat 8 beta

Tests for the dhcp fact on redhat 8 fail when enabled in the puppet-agent 5.5.x test suite. We've skipped this test in CI for now (see FACT-1905), but we'd like this to work correctly when the information is available.

FWIW, It looks like the redhat 8 pooler machines do have dhclient installed, but also have systemd-networkd in the mix; perhaps there is a new way to find this information.