Rework CI votes processing

1. Take into account only votes for the merged change requests.
2. Make processing compatible with the latest DriverLog: process comments
   only and allow multiple CIs share the same gerrit-id

NOTE: this patch introduces incompatible changes into data stored
in runtime storage. Full re-load is required.

Change-Id: Ic3e31d3cd3164c5ce786e0a19df2b4d0529ef40f

stackalytics/dashboard/parameters.py

@@ -54,7 +54,7 @@ METRIC_TO_RECORD_TYPE = {
     'resolved-bugs': ['bugr'],
     'members': ['member'],
     'person-day': ['mark', 'patch', 'email', 'bpd', 'bugf'],
-    'ci': ['ci_vote'],
+    'ci': ['ci'],
     'patches': ['patch'],
 }