Notification for Instance Exists not handled

[Peter Stachowski]

The new Notification framework hasn't been implemented for 'Trove Instance Exists' - the code below is saved here for reference (from trove/common/notification.py)

See the commit message in https://review.openstack.org/#/c/227870 for more details.

 # class TroveInstanceExists(TroveBaseTraits):
 #
 # '''
 # Additional traits for trove.instance.exists notifications that describe
 # instance action events
 #
 # This class should correspond to trove_instance_exists in
 # ceilometer/event_definitions.yaml
 # '''
 #
 # def __init__(self, **kwargs):
 # audit_start = kwargs['audit_start'],
 # audit_end = kwargs['audit_end'],
 #
 # super(TroveInstanceExists, self).__init__(**kwargs)
 #
 # self.payload.update({
 # 'audit_period_beginning': audit_start,
 # 'audit_period_ending': audit_end,
 # })
 #
 # def notify(self):
 # self.context = None
 # super(TroveInstanceExists, self).notify('exists', publisher_id=None)