[ovirt-users] user permissions

I'm trying to give a user the permissions to stop/start a specific server. This user is given the generic UserRole for the System. I tried to give him the roles : UserVmManager UserVmRunTimeManager UserInstanceManager InstanceCreator UserRole for that specific VM, I always get: query execution failed due to insufficient permissions. As soon as I give him the SuperUser role, he can stop/start it. What role should I give him for that VM ? I don't want to give the privilege to destroy the vm, or add disks. But he should be able to change the os settings too.