Add factilities to implement pytest.mark.parametrize and
pytest.fixtures patterns, which largely resemble things we are
already doing.
Ensure a facade is used, so that the test suite remains independent
of py.test, but also tailors the functions to the more limited
scope in which we are using them.
Additionally, create a class-based version that works from the
same facade.
Several old polymorphic tests as well as two of the sql test
are refactored to use the new features.
Change-Id: I6ef8af1dafff92534313016944d447f9439856cf
References: #4896
Mike Bayer
ed553fffd6