Fix tests with Plone 5.1

[mauritsvanrees]

See #43, which (for the moment) fixes the tests by doing Plone 5.0.x only. Otherwise you get this error:

$ bin/test 
Running Products.PloneTestCase.layer.PloneSite tests:
  Set up Testing.ZopeTestCase.layer.ZopeLite in 0.588 seconds.
  Set up Products.PloneTestCase.layer.ZCML in 4.935 seconds.
  Set up Products.PloneTestCase.layer.PloneSite Traceback (most recent call last):
  File "/Users/maurits/shared-eggs/cp27m/zope.testing-3.9.7-py2.7.egg/zope/testing/testrunner/runner.py", line 366, in run_layer
    setup_layer(options, layer, setup_layers)
  File "/Users/maurits/shared-eggs/cp27m/zope.testing-3.9.7-py2.7.egg/zope/testing/testrunner/runner.py", line 633, in setup_layer
    layer.setUp()
  File "/Users/maurits/shared-eggs/cp27m/Products.PloneTestCase-0.9.18-py2.7.egg/Products/PloneTestCase/layer.py", line 31, in setUp
    func(*args, **kw)
  File "/Users/maurits/shared-eggs/cp27m/Products.PloneTestCase-0.9.18-py2.7.egg/Products/PloneTestCase/setup.py", line 182, in setupPloneSite
    base_profile, extension_profiles).run()
  File "/Users/maurits/shared-eggs/cp27m/Products.PloneTestCase-0.9.18-py2.7.egg/Products/PloneTestCase/setup.py", line 236, in run
    self._abort()
  File "/Users/maurits/shared-eggs/cp27m/Products.PloneTestCase-0.9.18-py2.7.egg/Products/PloneTestCase/setup.py", line 395, in _abort
    transaction.abort()
  File "/Users/maurits/shared-eggs/cp27m/transaction-2.1.2-py2.7.egg/transaction/_manager.py", line 136, in abort
    return self.get().abort()
  File "/Users/maurits/shared-eggs/cp27m/transaction-2.1.2-py2.7.egg/transaction/_transaction.py", line 528, in abort
    reraise(t, v, tb)
  File "/Users/maurits/shared-eggs/cp27m/transaction-2.1.2-py2.7.egg/transaction/_transaction.py", line 514, in abort
    rm.abort(self)
  File "/Users/maurits/shared-eggs/cp27m/Products.CMFCore-2.2.12-py2.7.egg/Products/CMFCore/indexing.py", line 321, in tpc_abort
    self.queue.abort()
  File "/Users/maurits/shared-eggs/cp27m/Products.CMFCore-2.2.12-py2.7.egg/Products/CMFCore/indexing.py", line 237, in abort
    for name, util in sm.getUtilitiesFor(IIndexQueueProcessor):
  File "/Users/maurits/shared-eggs/cp27m/zope.interface-4.4.3-py2.7-macosx-10.12-x86_64.egg/zope/interface/registry.py", line 290, in getUtilitiesFor
    for name, utility in self.utilities.lookupAll((), interface):
AttributeError: 'RequestContainer' object has no attribute 'utilities'