Take advantage of the new build_short_uuid field.

Recently the elasticsearch schema was updated to include a
build_short_uuid field which has indexed the first 7 chars of the
build_uuid. This field is useful because it allows e-r to filter on that
field instead of searching on build_uuid.

Update e-r to filter on build_short_uuid which should make queries much
more performant. As part of this change replace variables named
short_build_uuid with build_short_uuid for consistency with the
elasticsearch schema.

Change-Id: Iae5323f3f5d2fd01f2c69f78b9403baf5ebafe85

elastic_recheck/bot.py

@@ -195,7 +195,7 @@ class RecheckWatch(threading.Thread):
 
                 for job in event.failed_jobs:
                     job.bugs = set(classifier.classify(
-                        event.change, event.rev, job.short_build_uuid))
+                        event.change, event.rev, job.build_short_uuid))
                 if not event.get_all_bugs():
                     self._read(event)
                 else: