Don't re-use resource-properties-data in backup stacks

When purging events we are only able to (efficiently) search for
references to resource properties data from events and resources in the
same stack. This results in foreign key constraint errors if the
resource properties data is referenced from a backup stack. To avoid
this, don't reuse resource properties data IDs after moving a resource
between the backup and main stacks, but duplicate the data instead.

Change-Id: I93329197c99a2dba37b0e1dbd7efe7b2b17bc036
Story: #2002643
Task: 22510

heat/engine/stack.py

@@ -734,6 +734,7 @@ class Stack(collections.Mapping):
 
     def add_resource(self, resource):
         """Insert the given resource into the stack."""
+        resource._rsrc_prop_data_id = None
         template = resource.stack.t
         resource.stack = self
         definition = resource.t.reparse(self.defn, template)