Initialize data field of cluster_policy after policy attaching
Initialize data field of cluster_policy after policy attaching

During the progress of policy attaching, some useful data could
be generated, e.g. ceilometer alarm ID for scaling policy, or lb
pool ID for lb policy. This patch allows attach method of policy
to return these data and then persist them using the data field of
cluster_policy object.

Change-Id: I7c5dd2535448d133deec73d983b16df90b7fe694

openstack/senlin,openstack/senlin,stackforge/senlin,openstack/senlin,tengqm/senlin-container,Alzon/senlin,stackforge/senlin,Alzon/senlin,tengqm/senlin-container