feat: option to prevent nova compute auto enable

why: for testing purpose, it can be helpful to have an option that a new novacomputenode is not enabled and running

solution: added a new field for the the novacompute options, that yaook is not set a compute node to enable, but to have it really work you have to set this option inside the DEFAULT Options: "enable_new_services = false" (source: https://docs.openstack.org/nova/wallaby/configuration/sample-config.html)