tools/libxl: Introduce LIBXL_CPUPOOL_POOLID_ANY

tools/libxl: Introduce LIBXL_CPUPOOL_POOLID_ANY

Callers to libxl_cpupool_create() can either request a specific pool
id, or request that Xen do it for them.  But at the moment, the
"automatic" selection is indicated by using a magic value, 0.  This is
undesirable both because it doesn't obviously have meaning, but also
because '0' is a valid cpupool (albeit one which at the moment can't
be changed).

Introduce a constant, LIBXL_CPUPOOL_POOLID_ANY, to indicate this
instead.  Still accept '0' as meaning "ANY" for backwards
compatibility.

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
[ wei: removed two trailing spaces ]
Signed-off-by: Wei Liu <wei.liu2@citrix.com>