Fixed stress test complaining about unicode

This fixes the stress test stopped working after this commit: https://github.com/cms-dev/cms/commit/6d694207d78e6ea1434f8104e2eaded97376cf39

The exception was:

Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 808, in \_\_bootstrap_inner
    self.run()
  File "cmstestsuite/StressTest.py", line 141, in run
    self.act()
  File "cmstestsuite/StressTest.py", line 205, in act
    base_url=self.base_url))
  File "cmstestsuite/StressTest.py", line 172, in do_step
    self.log.store_to_file(request)
  File "cmstestsuite/StressTest.py", line 94, in store_to_file
    request.store_to_file(fd)
  File "/usr/local/lib/python2.7/dist-packages/cms-1.1.0pre-py2.7.egg/cmstestsuite/web/\_\_init\_\_.py", line 183, in store_to_file
    print("Test type: %s" % (self.\_\_class\_\_.\_\_name\_\_), file=fd)
TypeError: must be unicode, not str