Reset notification errors to return 400
Reset notification errors to return 400

It seems the java api is returning 400 errors
for notification validation errors

Change-Id: Ib4b9252525db708df71eff15379c79b7ccaa702f

stackforge/monasca-api,stackforge/monasca-api,openstack/monasca-api,openstack/monasca-api,stackforge/monasca-api,sapcc/monasca-api,sapcc/monasca-api,openstack/monasca-api,stackforge/monasca-api,sapcc/monasca-api