Protobuf type for KPI slice metric type events

Change-Id: I397a2c480089aaf254070ba22695f3e63f9a8a69
diff --git a/shovel/main.py b/shovel/main.py
index 3854601..5d46810 100755
--- a/shovel/main.py
+++ b/shovel/main.py
@@ -131,16 +131,17 @@
 def _convert(msg):
     """Convert a graphite key value string to pickle."""
 
-    def extract_slice(ts, data):
-        for object_path, metrics in data.iteritems():
-            for metric_name, value in metrics.iteritems():
+    def extract_slice(ts, prefixes):
+        for object_path, metrics in prefixes.iteritems():
+            for metric_name, value in metrics['metrics'].iteritems():
                 path = '.'.join((object_path, metric_name))
                 yield (path, ts, value)
 
     assert isinstance(msg, dict)
     type = msg.get('type')
     if type == 'slice':
-        extractor, kw = extract_slice, dict(ts=msg['ts'], data=msg['data'])
+        extractor, kw = extract_slice, dict(ts=msg['ts'],
+                                            prefixes=msg['prefixes'])
     else:
         raise Exception('Unknown format')