Test: Trigger conditions is evaluated on subscription

It is expected that on subscription a trigger condition is evaluated and
the trigger fired if necessary. Currently evaluation is performed on
channel sampling and result in action only if the evaluation state flip.

This test hang if no evaluation is performed on notification client
subscription.

Ref #1102

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>