TST: QApplication doesn't quit early enough with PySide.

Fixes  #1628.  This commits adds a check in tests, to see if there's
already a QApplication and use it, instead of creating a new one each
time.

IPython/frontend/qt/console/tests/test_console_widget.py

@@ -14,7 +14,9 b' class TestConsoleWidget(unittest.TestCase):'
     def setUpClass(cls):
         """ Create the application for the test case.
         """
-        cls._app = QtGui.QApplication([])
+        cls._app = QtGui.QApplication.instance()
+        if cls._app is None:
+            cls._app = QtGui.QApplication([])
         cls._app.setQuitOnLastWindowClosed(False)
 
     @classmethod

IPython/frontend/qt/console/tests/test_kill_ring.py

@@ -14,7 +14,9 b' class TestKillRing(unittest.TestCase):'
     def setUpClass(cls):
         """ Create the application for the test case.
         """
-        cls._app = QtGui.QApplication([])
+        cls._app = QtGui.QApplication.instance()
+        if cls._app is None:
+            cls._app = QtGui.QApplication([])
         cls._app.setQuitOnLastWindowClosed(False)
 
     @classmethod