Use ddt for shib tests

@jbau, could you take a look at this? [Here are the `ddt` docs.](http://ddt.readthedocs.org/en/latest/index.html)
`ddt` treats each iteration as its own test, and will run the `setUp()` before and the `tearDown()` after each iteration. I'm not familiar with these tests, so I wanted to change them as little as possible, which is why I left this here. If the `tearDown` function takes care of this functionality, then yes, this code can (theoretically) be removed.