xen_common: Change xenConfigCopyStringInternal to use virConfGetValueString
xen_common: Change xenConfigCopyStringInternal to use virConfGetValueString

Signed-off-by: Fabiano Fidêncio <2931bae082ef9bc04523ba759c03a4778316d48f@redhat.com>
Reviewed-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>

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