Make all tests run

While working on https://github.com/atom/markdown-preview/issues/84 I noticed that not all tests in roaster were being run (because of the async nature of roaster when it loads contents from a file).

Also, the current tests check for string equality, where one string includes `/Users/garentorikian/Development/roaster/`. While I've considered renaming my account name to "garentorikian", making the tests more robust seems like a better approach. :smile:  (Also, there can be only one garentorikian!)

This PR makes all tests run (with a little help from spies :ghost:), and fixes tests so that they don't depend on machine account names (with a little help from cheerio).

cc @gjtorikian