Integrate sentry with the build worker.

util/exceptionlog.py

@@ -1,7 +1,15 @@
 from raven.contrib.flask import Sentry as FlaskSentry
 
+class FakeSentryClient(object):
+  def captureException(self, *args, **kwargs):
+    pass
+
+  def user_context(self, *args, **kwargs):
+    pass
+
 class FakeSentry(object):
-  pass
+  def __init__(self):
+    self.client = FakeSentryClient()
 
 class Sentry(object):
   def __init__(self, app=None):