domain_validate: use defines for cpu period and quota limits

domain_validate: use defines for cpu period and quota limits

Commints <bc760f4d7c4f964fadcb2a73e126b0053e7a9b06> and
<98a09ca48ed4fc011abf2aa290e02ce1b8f1bb5f> fixed the code to use
defines instead of magic numbers but missed this place.

Following commit <ed1ba69f5a8132f8c1e73d2a1f142d70de0b564a> changed
the cpu quota limit to reflect what kernel actually allows so using
the defines fixes XML validations as well.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>