restapi: fix cluster's schedulingpolicy back-compat

Ignores old (still supported) behavior (thresholds).

Change-Id: I4a5fa4d95bc55bed36d800532b81eb4340e4083d
Bug-Url: https://bugzilla.redhat.com/1118384
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>
(cherry picked from commit fb8cef7c16f47efca18da76297a80234042f220d)