test: run faster and cleanup after run

PR-URL: https://github.com/nodejs/node/pull/8848


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Matthew Loring <mattloring@google.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>