vbox: Close media when undefining domains
vbox: Close media when undefining domains

When registering a VM we call OpenMedium on each disk image which adds it
to vbox's global media registry. Therefore, we should make sure to call
Close when unregistering VM so we cleanup the media registry entries
after ourselves - this does not remove disk image files. This follows
the behaviour of the VBoxManage unregistervm command.

jardasgit/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,jardasgit/libvirt,jardasgit/libvirt,nertpinx/libvirt,zippy2/libvirt,crobinso/libvirt,fabianfreyer/libvirt,zippy2/libvirt,libvirt/libvirt,andreabolognani/libvirt,crobinso/libvirt,andreabolognani/libvirt,olafhering/libvirt,zippy2/libvirt,jfehlig/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,olafhering/libvirt,olafhering/libvirt,eskultety/libvirt,zippy2/libvirt,libvirt/libvirt,eskultety/libvirt,nertpinx/libvirt,eskultety/libvirt,nertpinx/libvirt,jfehlig/libvirt,eskultety/libvirt,libvirt/libvirt,libvirt/libvirt,nertpinx/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,eskultety/libvirt,crobinso/libvirt,jfehlig/libvirt,olafhering/libvirt,jardasgit/libvirt,crobinso/libvirt