Put back nr.guid if synthetics resource id

Author: hmstepanek

newrelic/core/transaction_node.py

@@ -463,6 +463,8 @@ def _add_if_not_empty(key, value):
         if self.errors:
             intrinsics["error"] = True
 
+        if self.synthetics_resource_id:
+            intrinsics["nr.guid"] = self.guid
         if self.parent_tx:
             intrinsics["parentId"] = self.parent_tx