libxl: turn NUMA placement misconfigs into warnings

libxl: turn NUMA placement misconfigs into warnings

instead than errors. More specifically, in libxl,
b_info->numa_autoplacement is meant as a way to
disable automatic NUMA placement, if one does not
want it to happen. It is, however, useful for
consistency checking as well, i.e., to ensure that
the user provided configuration (such as, for instance,
vcpu hard or soft affinity) and NUMA placement itself
will not clash.

However, right now, if such a clash happens we abort
domain creation and error out, which is too much! It
is, in fact, enough to infom the user/caller that NUMA
placement won't be performed, with a WARN, and that's
what this commit does.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>