3 Notification support for host aggregate related operation

Currently in OpenStack, when customer create/delete host aggregation, add host to/remove host from host aggregation, OpenStak did not generate notifications for those operations. If one component wants to do some operations based on host aggregation update, then the component need to query DB to get the status of host aggregation and this is not real-time.
It is better that the component can get notification for aggregation related operations so as to make related component can response on time based on aggregation operations.

Solution Description
Add notification for the following operations related to host aggregation
a) Send notification when create a new host aggregation
b) Send notification when delete a host aggregation
c) Send notification when add host to a host aggregation
d) Send notification when delete host from host aggregation
e) Send notification when update host aggregation for aggregate name and available zone
f) Send notification when update host aggregation meta data