Fix Nova aggregate alarms

Set 'no_data' policy to OKAY in case there's no aggregate defined.

Change-Id: If28f4c060db7922dbdcf73c4aeba54b3fefd6082
diff --git a/nova/meta/heka.yml b/nova/meta/heka.yml
index 0f2f19c..7452e9b 100644
--- a/nova/meta/heka.yml
+++ b/nova/meta/heka.yml
@@ -245,6 +245,7 @@
     nova_aggregates_free_memory_warning:
       description: 'The nova aggregates free memory percent is low'
       severity: warning
+      no_data_policy: okay
       rules:
       - metric: openstack_nova_aggregate_free_ram_percent
         group_by: [aggregate]
@@ -256,6 +257,7 @@
     nova_aggregates_free_memory_critical:
       description: 'The nova aggregates free memory percent is too low'
       severity: critical
+      no_data_policy: okay
       rules:
       - metric: openstack_nova_aggregate_free_ram_percent
         group_by: [aggregate]