Before this patch all ERP5 SlapOS Integration tests only run with ZEO
storage. We should also run them against NEO, because we are using
ERP5 with NEO in SlapOS.

In order to do so we implemented parameterized test classes for our ERP5
integration tests. Each test case can be configured via its __test_matrix__
attribute. A test matrix is a dict which maps the flavoured class name suffix to
a tuple of parameters. A parameter is a function which receives the
instance_parameter_dict and modifies it in place. You can use the
'matrix' helper function to construct a test matrix. If .__test_matrix__
is 'None' the test case is ignored.

/reviewed-by @kirr & @jerome
/reviewed-on nexedi/slapos!1306