Configure pytest to look for tests in "test" directory

Thus avoiding default value of posargs in tox's test environment.

tox.ini

@@ -6,7 +6,7 @@ deps =
   pytest
   https://hg.logilab.org/master/cubes/sioc/archive/default.tar.bz2
 commands =
-  {envpython} -m pytest {posargs:test}
+  {envpython} -m pytest {posargs}
 
 [testenv:flake8]
 skip_install = true
@@ -28,3 +28,4 @@ exclude = cubicweb_blog/__pkginfo__.py,cubicweb_blog/migration/*,test/data/*,.to
 
 [pytest]
 python_files = *test_*.py
+testpaths = test