Cleanup in tests.helpers.
Cleanup in tests.helpers.

* Use single-quoted string conforming to the rest of the file [PEP8]
* Use format instead of % operator
* Remove bad and ugly try-catchall statements.
  (cuz @vecna just wanna catch'em all)
  http://www.youtube.com/watch?v=SVp-zIONsrs

vodkina/GlobaLeaks,vodkina/GlobaLeaks,vodkina/GlobaLeaks,vodkina/GlobaLeaks