fix tests, use pytest

We currently test with unparallelized builds,
because there are apparently some race conditions
in the test suite, which I can't trigger locally
but happen on travis.

Squashed commit of the following:

commit 7dceb6dd3a1bdbc39688258bc4dff6eee685a33b
Author: Maximilian Hils <git@maximilianhils.com>
Date:   Mon Sep 21 23:00:24 2015 +0200

    disable parallelized tests

commit fc0c3f12ee9259162e83026851362925d93b69f2
Author: Maximilian Hils <git@maximilianhils.com>
Date:   Mon Sep 21 22:49:19 2015 +0200

    fix tests

commit baba3ca5ef49bdbd7aad14f1bf0626738fa3d21c
Author: Maximilian Hils <git@maximilianhils.com>
Date:   Mon Sep 21 22:28:20 2015 +0200

    fix tests, use py.test

1 files changed, 3 insertions, 2 deletions

diff --git a/setup.py b/setup.py
index 041b164d..7acb23b5 100644
--- a/setup.py
+++ b/setup.py
@@ -56,8 +56,9 @@ setup(
     extras_require={
         'dev': [
             "mock>=1.0.1",
-            "nose>=1.3.0",
-            "nose-cov>=1.6",
+            "pytest>=2.8.0",
+            "pytest-xdist>=1.13.1",
+            "pytest-cov>=2.1.0",
             "coveralls>=0.4.1"
         ]
     }