If you want to add host running Fedora 28, you need to do few manual steps:

1. Add hosts fail to configure the firewall

Do not check the "Configure filewall" checkbox

Adding host will fail because engine cannot communicate with vdsm.

Fix - disable the firewall on the host.
$ iptables -F

There is probably a better way, but I did not find it yet :-)

Sandro, do we have an update about this?

2. Engine fail in Host.getCapabilties 

Libvirt changed the location and format of this file. This will cause Host.getCapabilties 
to fai, and the host will become "Unassigned"

This is a new issue revealed by updating our virt-preview repo this week.

Fix - install old cpu_map.xml

Engine should retry and succeed after that.

3. Sanlock fail to write to its pid file, connecting to storage fail

Fix - set selinux to permissive mode
$ setenforce 0

To make this persistent edit /etc/selinux/config

We have a bug for this.

After that you should have a working system.