tox: Update pytest-qt to 1.9.0.

- Exception capturing now happens as early/late as possible in order to catch
  all possible exceptions (including fixtures).
- Widgets registered by qtbot.addWidget are now closed before all other
  fixtures are tear down.
- qtbot now has a new wait method which does a blocking wait while the event
  loop continues to run, similar to QTest::qWait.
- raise RuntimeError instead of ImportError when failing to import any Qt
  binding: raising the latter causes pluggy in pytest-2.8 to generate a subtle
  warning instead of a full blown error.

tox.ini

@@ -18,7 +18,7 @@ deps =
     py==1.4.30
     pytest==2.7.3  # rq.filter: <2.8.0
     pytest-capturelog==0.7
-    pytest-qt==1.8.0
+    pytest-qt==1.9.0
     pytest-mock==0.8.1
     pytest-html==1.7
     pytest-faulthandler==1.0.1