In order to be able to globally enable notification reporting for all services,
without an need to have ceilometer deployed or bunch of overrides for each
service, we add `oslomsg_notify_enabled` variable that aims to control
behaviour of enabled notifications.
Presence of ceilometer is still respected by default and being referenced.
Potential usecase are various billing panels that do rely on notifications
but do not require presence of Ceilometer.
Change-Id: I63f5b887608f4c43e1fa953fbc194414d9bebc30
5a692ce993