Disable session data manager in unit tests

This fixes test_report_view (testDeferredStyle).

product/ERP5Type/tests/runUnitTest.py

@@ -451,6 +451,9 @@ def runUnitTestList(test_list, verbosity=1, debug=0, run_only=None):
   os.chdir(tests_home)
 
   from Products.ERP5Type.patches import noZopeHelp
+  from OFS.Application import AppInitializer
+  AppInitializer.install_session_data_manager = lambda self: None
+
   # import ERP5TypeTestCase before calling layer.ZopeLite.setUp
   # XXX What if the unit test itself uses 'onsetup' ? We should be able to call
   #     remaining 'onsetup' hooks just before executing the test suite.