Enable unittests during package build

Hi Holger,

i try to address the points you brought up in the last pull-request [1]: 

* Added needed Build-Depends
* Re-enable unittests in debian/rules
* Don't create coverage files during package build

This enables the unittests now for every package build and use nosetests for it (but don't create coverage reports). I added python-nose (and a bunch more) to the Build-Depends. Is this ok? You wrote about "something like Build-recommends" so did you think it would be to much to run the tests in every build?

Best wishes,
Matthias 
[1] https://github.com/h01ger/piuparts/pull/1