xen/domain: Call sched_destroy_domain() in the domain_create() error path

xen/domain: Call sched_destroy_domain() in the domain_create() error path

If domain_create() fails, complete_domain_destroy() doesn't get called,
meaning that sched_destroy_domain() is missed.  In practice, this can only
fail because of exceptional late_hwdom_init() issues at the moment.

Make sched_destroy_domain() idempotent, and call it in the fail path.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>