tools: Fix wild memory allocations from c/s 250f0b4 and 85d78b4

tools: Fix wild memory allocations from c/s 250f0b4 and 85d78b4

These changesets cause the respective libxc functions to unconditonally
dereference their max_cpus/nodes parameters as part of initial memory
allocations.  It will fail at obtaining the correct number of cpus/nodes from
Xen, as the guest handles will not be NULL.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>