tools: Rework xc_domain_create() to take a full xen_domctl_createdomain

tools: Rework xc_domain_create() to take a full xen_domctl_createdomain

In future patches, the structure will be extended with further information,
and this is far cleaner than adding extra parameters.

The python stubs are the only user which passes NULL for the existing config
option (which is actually the arch substructure).  Therefore, the #ifdefary
moves to compensate.

For libxl, pass the full config object down into
libxl__arch_domain_{prepare,save}_config(), as there are in practice arch
specific settings in the common part of the structure (flags s3_integrity and
oos_off specifically).

No practical change in behaviour.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>