[libvirt] Libvirt xl to xml converter only picks up first occurrence of an option

Hi Jim I discovered that libvirt's native config file to xml converter for libxl only pick up the first occurrence of an option. For example in a xl cfg file: extra = "abc" ... extra = "def" xl will pick up "def" because that shows up later and takes precedence, while the converter picks up "abc". I think this is a bug in the converter and should be fixed. Thanks Wei.