rebase: Specify value_meta for usage summary

Move the usage summary from a dimension to the value_meta for
the same reasons as the flavor resources.

Author: dougszumski

cron/example.sh

@@ -241,16 +241,18 @@ def get_key(allocation):
 
             if key_name:
                 dimensions[name_key] = key_name
-            dimensions['usage_summary'] = usage
+            value_meta = {'usage_summary': usage}
             dimensions['version'] = 2.0
 
             metrics_to_send.append(metrics.Metric(
                 name="usage.%s.count" % group_by,
                 value=grouped_usage['Count'],
+                value_meta=value_meta,
                 dimensions=dimensions))
             metrics_to_send.append(metrics.Metric(
                 name="usage.%s.days.count" % group_by,
                 value=grouped_usage_days['Count'],
+                value_meta=value_meta,
                 dimensions=dimensions))
 
     # Sort my largest current usage first