HtmlProxyRenderTest.test_blacklist can fail

[kmike]

I can't reproduce it myself, but this failure happened:

======================================================================
FAIL: test_blacklist (splash.tests.test_proxy.HtmlProxyRenderTest)
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Traceback (most recent call last):
  File "/var/lib/buildbot/slave/builders/splash/build/splash/tests/test_proxy.py", line 72, in test_blacklist
    self.assertProxied(frame['html'])
  File "/var/lib/buildbot/slave/builders/splash/build/splash/tests/test_proxy.py", line 94, in assertProxied
    assert 'PROXY_USED' in html
AssertionError: 
-------------------- >> begin captured logging << --------------------
requests.packages.urllib3.connectionpool: INFO: Starting new HTTP connection (1): localhost
requests.packages.urllib3.connectionpool: DEBUG: "GET /render.json?url=http%3A%2F%2Flocalhost%3A8998%2Fiframes&html=1&iframes=1&proxy=test HTTP/1.1" 200 None
--------------------- >> end captured logging << ---------------------

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[kmike]

I haven't seen this failure since then, it could have been related to #30 which is fixed.