Benp/paver tests

@clytwynec @muhammad-ammar 

Could you take a look?

I'm leaving out the subdir problem as that's something we're still vetting out. Note as well that we are not looking at coverage of paver right now; that's still going to be ignored at this point.

Ben

That seems fine.  We should probably update this docstring to specify that though... https://github.com/edx/edx-platform/blob/master/pavelib/tests.py#L82