ncm-opennebula: add support for OpenNebula

@piojo for now, we use the `config-templates` repo to unittest the TT files. once the nwe test infrastructure is part of `Test::Quattor`, the TT files, schema and config and their tests will move here. that's what the TODO is about (and we hope to have this all done for 14.12). this is all part of https://github.com/quattor/configuration-modules-core/issues/348