SCVMM: Virtual DVD drive support fixes

This PR includes the following:
1) Support for virtual dvd drives for templates
2) Graceful handling of VMs without a virtual DVD mounted. VMM server version 3.1.6 returns an empty hash which caused the parser to blow up. More recent versions of VMM server return a hash containing values that indicate no DVD has been configured.

https://bugzilla.redhat.com/show_bug.cgi?id=1166861