conf: use disk source accessors in vbox/
conf: use disk source accessors in vbox/

Part of a series of cleanups to use new accessor methods.

* src/vbox/vbox_tmpl.c (vboxDomainGetXMLDesc, vboxAttachDrives)
(vboxDomainAttachDeviceImpl, vboxDomainDetachDevice): Use
accessors.

Signed-off-by: Eric Blake <a9da18479c871fe903d9590822cfe2629c6a4d11@redhat.com>

agx/libvirt,olafhering/libvirt,taget/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,zippy2/libvirt,libvirt/libvirt,datto/libvirt,libvirt/libvirt,rlaager/libvirt,nertpinx/libvirt,elmarco/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,taget/libvirt,rlaager/libvirt,agx/libvirt,fabianfreyer/libvirt,datto/libvirt,andreabolognani/libvirt,datto/libvirt,jardasgit/libvirt,crobinso/libvirt,shugaoye/libvirt,rlaager/libvirt,elmarco/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,shugaoye/libvirt,elmarco/libvirt,olafhering/libvirt,jardasgit/libvirt,zippy2/libvirt,olafhering/libvirt,andreabolognani/libvirt,nertpinx/libvirt,taget/libvirt,eskultety/libvirt,crobinso/libvirt,eskultety/libvirt,VenkatDatta/libvirt,eskultety/libvirt,elmarco/libvirt,VenkatDatta/libvirt,rlaager/libvirt,nertpinx/libvirt,crobinso/libvirt,jfehlig/libvirt,jfehlig/libvirt,eskultety/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,crobinso/libvirt,taget/libvirt,libvirt/libvirt,nertpinx/libvirt,nertpinx/libvirt,libvirt/libvirt,datto/libvirt,rlaager/libvirt,agx/libvirt,olafhering/libvirt,shugaoye/libvirt,elmarco/libvirt,andreabolognani/libvirt,jardasgit/libvirt,zippy2/libvirt,zippy2/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,taget/libvirt,agx/libvirt,eskultety/libvirt,VenkatDatta/libvirt,agx/libvirt,shugaoye/libvirt,shugaoye/libvirt,datto/libvirt,fabianfreyer/libvirt