xen: use typical allocations

xen: use typical allocations

The next patch will add a syntax check that flags this usage in xen
as awkward - while it was valid memory management, it was very hard
to maintain.  Swapping to a more traditional allocation may be a bit
slower, but easier to understand.

* src/xen/xend_internal.c (xenDaemonListDomainsOld): Use two-level
allocation, rather than abusing allocation function.
(xenDaemonLookupByUUID): Update caller.