add ability to print out benchmark report at the end

The report looks like this:

```
Benchmark Report:
Ordered by deploy sequence:
  deploy:notify:start        :  0 mins and  4 secs
  deploy:finalize_update     :  0 mins and 26 secs
  symlinks:to_release        :  0 mins and  2 secs
  asset_packager:to_release  :  0 mins and  0 secs
  thinking_sphinx:configure  :  0 mins and  0 secs
  newrelic:notice_deployment :  0 mins and  5 secs
  deploy:update_code         :  2 mins and 22 secs
  deploy:create_symlink      :  0 mins and 24 secs
  deploy:update              :  3 mins and 46 secs
  delayed_job:restart        :  0 mins and  1 secs
  deploy:restart             :  0 mins and 18 secs
  deploy:notify:stop         :  0 mins and  1 secs
  deploy:cleanup             :  0 mins and 14 secs
Ordered by slowest:
  deploy:update              :  3 mins and 46 secs
  deploy:update_code         :  2 mins and 22 secs
  deploy:finalize_update     :  0 mins and 26 secs
  deploy:create_symlink      :  0 mins and 24 secs
  deploy:restart             :  0 mins and 18 secs
  deploy:cleanup             :  0 mins and 14 secs
  newrelic:notice_deployment :  0 mins and  5 secs
  deploy:notify:start        :  0 mins and  4 secs
  symlinks:to_release        :  0 mins and  2 secs
  deploy:notify:stop         :  0 mins and  1 secs
  delayed_job:restart        :  0 mins and  1 secs
  asset_packager:to_release  :  0 mins and  0 secs
  thinking_sphinx:configure  :  0 mins and  0 secs
```