TemporaryJobs no longer throws an exception if it encounters a directory

There shouldn't be any directories in the temp directory, but if we
should just ignore it if one is there. Also, TemporaryJobsTest now
creates it's own directory under the main temporary directory so
that is not effected by other tests using the temp directory.
Merge pull request #75 from spotify/rculbertson/temp-jobs-test-fix

TemporaryJobs no longer throws an exception if it encounters a directory