TST: skip the test if a known problem with Python 2.6 is detected

As was original "discovered" while running tests on OSX with python2.6:
http://nipy.bic.berkeley.edu/builders/fail2ban-py2.7-osx-10.6_master/builds/6/steps/shell_2/logs/stdio

I was not sure if we should just indeed just skip it here or actually add some similar basic test into fail2ban-client to warn users trying to run fail2ban... but then guessed that if it fails to start for them on such rare systems -- then can bother to look into the log... although it would be not that enlightening about the problem