Export add integration test

This PR:

* Adds [integration tests for the export functionality](https://github.com/msabramo/honcho/blob/export_add_integration_test/honcho/test/integration/test_export.py) (4b33c2c)
* Tweaks a few things so that tests pass consistently. E.g.:
    * Sort dictionary keys to get consistent ordering from run to run (e32be90)
    * Use `items` in place of `iteritems` in upstart template for Python 3 compatibility (3e9c2d9)
    * Apply fix from https://github.com/nickstenning/honcho/pull/102 so that we don't get spurious test failures that confuse things. (5148677)

```
$ tox -e py26,py27,py32,py33,py34,lint
...
  py26: commands succeeded
  py27: commands succeeded
  py32: commands succeeded
  py33: commands succeeded
  py34: commands succeeded
  lint: commands succeeded
  congratulations :)
```