[#1988] Record memory usage for tests.


Problem description
===================


This is initial support in empirical for getting some data for memory usage.


Changes description
===================

When nose-runner exists, it will print the maximum memory used by the process.

I have also created an experimental nose plugin to measure peak memory before and after test.
This is not very helpful, since we need actual memory.



How to try and test the changes
===============================

reviewers @alibotean 
Check that code is ok.

run paver test --with-memory-usage

use latest empirical in you project.