Fix bug where dimension value is not a string

This caused the Monasca API to reject the metric.

Author: dougszumski

os_capacity/utils.py

@@ -242,7 +242,7 @@ def get_key(allocation):
             if key_name:
                 dimensions[name_key] = key_name
             value_meta = {'usage_summary': usage}
-            dimensions['version'] = 2.0
+            dimensions['version'] = '2.0'
 
             metrics_to_send.append(metrics.Metric(
                 name="usage.%s.count" % group_by,