Make tests a bit less leaky

[chriskuehl]

We have a problem on our Jenkins CI where sometimes the builddeb-docker stage hangs indefinitely and leaves processes running taking up CPU:

21:51:21 make[1]: Entering directory '/mnt'
21:51:21 find . -name '*.pyc' -delete
21:51:21 find . -name '__pycache__' -delete
21:51:21 PATH=.:$PATH py.test tests/
21:51:21 ============================= test session starts ==============================
21:51:21 platform linux2 -- Python 2.7.12rc1, pytest-2.9.2, py-1.4.31, pluggy-0.3.1
21:51:21 rootdir: /mnt, inifile: pytest.ini
21:51:21 collected 173 items
21:51:21 
23:50:07 tests/child_processes_test.py .............Build timed out (after 120 minutes). Marking the build as aborted.

We don't know exactly what tests are being failed to investigate further, so let's solve the immediate problem by adding a timeout (should prevent leaking containers) and make py.test verbose so we can see what test is failing to try to investigate further.

[bukzor]