test suite requires a proxy that is external to test environment

cd tests; make

you get this failure:

======================================================================
FAIL: test_url_downloadable (__main__.TestMetaReleaseCore)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "./test_meta_release_core.py", line 54, in test_url_downloadable
    "download with proxy %s failed" % os.environ["http_proxy"])
AssertionError: download with proxy http://localhost:3128/ failed

I think the problem is that the tests expect a local mirror proxy to be running, and that the proxy be started outside of the test environment (i.e. manually, before running 'make'). This makes the test too fragile to rely on.

Any required proxy should be started and shutdown in the test suite itself.