Decouple KVM software release and frontend.

Frontend may be provided by another software release.

software/kvm/instance-kvm.cfg

@@ -127,19 +127,21 @@ db-path = $${rootdirectory:srv}/slapmonitor_database
 
 [request-slave-frontend]
 recipe = slapos.cookbook:request
-software-url = $${slap-connection:software-release-url}
+software-url = $${slap-connection:frontend-software-url}
 server-url = $${slap-connection:server-url}
 key-file = $${slap-connection:key-file}
 cert-file = $${slap-connection:cert-file}
 computer-id = $${slap-connection:computer-id}
 partition-id = $${slap-connection:partition-id}
 name = SlaveFrontend
-software-type = frontend
+software-type = $${slap-connection:frontend-software-type}
 slave = true
 config = host port
 config-host = $${novnc-instance:ip}
 config-port = $${novnc-instance:port}
 return = url resource port domainname
+sla = instance_guid
+sla-instance_guid = $${slap-parameter:frontend-instance-guid}
 
 [publish-kvm-backend-connection-information]
 recipe = slapos.cookbook:publish