* add progress bar in cache.download_file()
* refactoring: rename cache-related commands to cache-* for consistency
refactoring: actually use FIXT_CACHE_DIR everywhere
* fix test suite
* add jenkinsfarm/slots tests
* cleaning (inherit TestJenkinsBase)

25b06c39bad moved tests from test/ to test/commands, which changed the order in
which tests are run by setup.py: test.commands.test_base ran after
test.test_helpers which was installing our MockHTTPHandler as the default url
opener (urllib2.install_opener()) thus breaking urllib2 and more specifically
test_cache_update with:
URLError: <urlopen error unknown url type: http>