add missing macro load_grains_file

Change-Id: I025e8b291033b30ac7edb22b04b9050904775966
diff --git a/heka/map.jinja b/heka/map.jinja
index 4357d2f..45c6956 100644
--- a/heka/map.jinja
+++ b/heka/map.jinja
@@ -1,3 +1,4 @@
+{%- macro load_grains_file(grains_fragment_file) %}{% include grains_fragment_file ignore missing %}{% endmacro %}
 {%- load_yaml as server_defaults %}
 Debian:
   pkgs: