explain payload inheritance in notification devref
explain payload inheritance in notification devref

During the implementation of I1c8c038078bbe1a5914a92d44b3e977287294a88
we realized that the inheritance used in the notification payload
classes has some drawbacks. When we need to introduce new leaf classes
the content of the nova.obj_name field will change in the emited
payload. This should be avoided if possible. If this cannot be avoided
and the only change is the renaming then the version of the new
payload shall be the same as the old payload was before the rename.
If the renaming involves any other changes on the payload (e.g. adding
new fields) then the version of the new payload shall be higher than
the old payload was.

Change-Id: Ie8c9317892f5593d473067d5dfc300a7e98795c5

gooddata/openstack-nova,mikalstill/nova,openstack/nova,gooddata/openstack-nova,klmitch/nova,mikalstill/nova,openstack/nova,openstack/nova,rahulunair/nova,gooddata/openstack-nova,mahak/nova,mikalstill/nova,rahulunair/nova,klmitch/nova,phenoxim/nova,phenoxim/nova,gooddata/openstack-nova,klmitch/nova,mahak/nova,mahak/nova,rahulunair/nova,klmitch/nova