RHEL8 Avahi discovery requires EPEL8 released

[lpramuk]

IP discovery in our automation relies on Avahi and needs also nss-mdns so that it can name resolve avahi records.

This package lives in EPEL, now when RHEL8 is out there is no el8 nss-mdns which expected to be provided by EPEL8.

Until EPEL8 provides us the package we can hopefully work around the problem, el7 rpm seems to work on RHEL8, ldd shows no unresolved library deps.