Ported tests to plone.app.testing.

This PR ports the tests of p.a.versioningbehavior to p.a.testing, based on the changes in https://github.com/plone/Products.CMFEditions/pull/19 which does the same for CMFEditions.

This requires Plone 5 and the branch of the [CMFEditions pull-request](https://github.com/plone/Products.CMFEditions/pull/19).

/cc @tomgross 
This dependency is probably wrong; I had a custom buildout and got:

```python
  File "/Users/jone/projects/python/cache/eggs/plone.app.upgrade-1.3.8-py2.7.egg/plone/app/upgrade/v30/__init__.py", line 2, in <module>
    import alphas
  File "/Users/jone/projects/python/cache/eggs/plone.app.upgrade-1.3.8-py2.7.egg/plone/app/upgrade/v30/alphas.py", line 91, in <module>
    from Products.ATContentTypes.interfaces import IFactoryTool
ZopeXMLConfigurationError: File "/Users/jone/projects/python/cache/eggs/plonetheme.barceloneta-1.6.1-py2.7.egg/plonetheme/barceloneta/configure.zcml", line 11.2-11.41
    ZopeXMLConfigurationError: File "/Users/jone/projects/python/cache/eggs/plone.app.theming-1.2.1-py2.7.egg/plone/app/theming/configure.zcml", line 19.4-19.44
    ZopeXMLConfigurationError: File "/Users/jone/projects/python/cache/eggs/plone.app.registry-1.2.3-py2.7.egg/plone/app/registry/configure.zcml", line 12.4-12.34
    ZopeXMLConfigurationError: File "/Users/jone/projects/python/cache/eggs/plone.app.registry-1.2.3-py2.7.egg/plone/app/registry/browser/configure.zcml", line 6.4-6.43
    ZopeXMLConfigurationError: File "/Users/jone/projects/python/cache/eggs/plone.app.z3cform-1.0.1-py2.7.egg/plone/app/z3cform/configure.zcml", line 10.2-10.41
    ZopeXMLConfigurationError: File "/Users/jone/projects/python/cache/eggs/plone.app.widgets-1.7.0-py2.7.egg/plone/app/widgets/configure.zcml", line 14.2-14.41
    ZopeXMLConfigurationError: File "/Users/jone/projects/python/cache/eggs/Products.CMFPlone-5.0a3-py2.7.egg/Products/CMFPlone/configure.zcml", line 31.2-31.86
    ZopeXMLConfigurationError: File "/Users/jone/projects/python/cache/eggs/plone.app.upgrade-1.3.8-py2.7.egg/plone/app/upgrade/configure.zcml", line 7.4-7.30
    ZopeXMLConfigurationError: File "/Users/jone/projects/python/cache/eggs/plone.app.upgrade-1.3.8-py2.7.egg/plone/app/upgrade/v25/configure.zcml", line 13.8-16.14
    ImportError: No module named ATContentTypes.interfaces
```

How should this work?