generator/host: Respect host_class for VM hosts

generate-icinga-generic-host.py

@@ -247,6 +247,9 @@ def create_icinga2_host_object_from_netbox(netbox, device_name):
                 ssh_port
                 )
 
+    if device.device_role.slug == "vm-host":
+        host.host_class = "vm-host"
+
     for ip4 in non_uplink_ip4s:
         host.add_ip(ip4)
     for ip6 in non_uplink_ip6s: