[Libguestfs] [FOR REVIEW ONLY] ESX work in progress

The following patches are where I'm currently at with ESX support. I can now import a domain from ESX along with its storage. Note that I'm not yet doing any conversion. In fact, I've never even tested past the import stage (I just had an exit in there). The meat is really in the 4th patch. The rename of MetadataReader->Connection was because the Connection is now really providing the whole guest, rather than just its metadata. I intend to add more transfer methods once ESX conversion is working. A copy method for LibVirtXML is required at least. _storage_iterate in Sys::VirtV2V::Connection does interesting things with the domain's storage devices. I'd especially appreciate a close look there. Matt