Prevent Messaging to resend failed notifications

Infinite retrying to send notification may cause osprofiler to block, if
transport is not configured correctly. So the easiest way to avoid this sort
of blocks is to set retry=0 at notifier configuration.

Change-Id: I5a4b75905dc8d63b612e193805bae28616e425a7
Fix wrong code duplication in utils.itersubclasses()

Change-Id: Ic34be7cb10b5aba723394e06ddff69cb09fe698d
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Merge "Prevent Messaging to resend failed notifications"