vbox: Fix resource leak
vbox: Fix resource leak

The @disk was allocated, filled in, and consumed on the normal path,
but for error/cleanup paths it would be leaked.  Rename to newHardDisk
and manage properly.

Found by Coverity

Signed-off-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>
Reviewed-by: Katerina Koukiou <e327f8a3293ed5cbf737faab85e97cd2d0b8b9c3@redhat.com>

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