Improves JobTest code
Memoize for correctness
Try to run with random name to deal with Hadoop race
Try again
Merge pull request #612 from twitter/random-user

Try to run with random name to deal with Hadoop race
Merge branch 'develop' of github.com:twitter/scalding into jobtestcase
Merge pull request #604 from twitter/jobtestcase

Improves JobTest code