Added test for upgradeStep to 4308 and tested the addDefaultPlonePasswordPolicy handler

Added test for recent pull request (https://github.com/plone/plone.app.upgrade/pull/12).

Hope the format is OK...  Anyway I do not know how tests are supposed to pass because when I launch it, I have 147 tests with 14 failures, regarding tests to v33, v41, ... wich looks possible...  Mine pass, but what is really launched by robot and so on?

Thank you!

Gauthier