Add lifecycle hook spec
Add lifecycle hook spec

The AWS autoscaling service provides a 'lifecycle hook' feature that Senlin
currently lacks. Lifecycle hooks during scaling operations allow the user or
an application to perform custom setup or clean-up of instances.

Change-Id: I61ddf4b5e560f3c913fa962665d43048090ef3ed

openstack/senlin,openstack/senlin,openstack/senlin,stackforge/senlin,stackforge/senlin