[WIP] Add py.test package

Currently it fails to run:
```
$ py.test --version
Traceback (most recent call last):
  File "/nh/nest/u/ondrej/repos/hashstack/default/bin/py.test", line 8, in <module>
    from pkg_resources import load_entry_point
  File "/tmp/bld2/profile/xhyi5yguwlf4/lib/python2.7/site-packages/pkg_resources.py", line 2749, in <module>
    working_set = WorkingSet._build_master()
  File "/tmp/bld2/profile/xhyi5yguwlf4/lib/python2.7/site-packages/pkg_resources.py", line 444, in _build_master
    ws.require(__requires__)
  File "/tmp/bld2/profile/xhyi5yguwlf4/lib/python2.7/site-packages/pkg_resources.py", line 725, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/tmp/bld2/profile/xhyi5yguwlf4/lib/python2.7/site-packages/pkg_resources.py", line 628, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: py>=1.4.20
```
Not sure what's going on yet.