crontabberise drop_old_partitions; bug 1014128; attempt #2

This addresses bug 1014128. Again. (Previous attempt at rebasing was a horrible disaster. :unamused:) 

`?r` @peterbe and/or @rhelmer :revolving_hearts: 
```eq_``` is nose shorthand for ```assert```:
http://nose.readthedocs.org/en/latest/testing_tools.html#nose.tools.eq_