Improve the log to avoid unexpected ERROR
Improve the log to avoid unexpected ERROR

When notification pipeline and pooling are both enabled, the method
'post' of NotifierDriver will be called two times. One for normal
SubscriptionController and one for pooling.SubscriptionController.
So a check was added to avoid the notifition is sent two times, but
unfortunately an unintentional error was introduced. This patch fixes
it by refactoring the condition checking.

Change-Id: Ie22748e86a50b7d91f24707b0c5a3ab718f005a2

openstack/zaqar,openstack/zaqar,openstack/zaqar,openstack/zaqar