bugfix: email notifications are duplicated
bugfix: email notifications are duplicated

Once an email notification is successfully dispatched no more
attempts are made to send the email.

Change-Id: Iebeb0badee9004c743e95be6836f2b1df42fcb9c

stackforge/poppy,openstack/poppy,openstack/poppy,stackforge/poppy,stackforge/poppy,openstack/poppy