Support pytest test parametrization via nanaimo.cfg

[kcandow]

Parametrizing Pytest tests and fixtures makes testing different setups and configuration more natural. The pytest concept of parametrizing translates well to the nanaimo concept of testing different hardware configurations on a single test rig.

Assume that a test rig may have any number of widgets that all respond to the foo test. A parametrized test would look like this:

@pytest.mark.asyncio
@pytest.mark.parametrize("widget_id", ["w0", "w1", "w2"])
async def test_foo(foo_fixture):
    assert_success(await foo_fixture.gather(dut=widget_id))

Ideally, the list of widgets (w0, w1, w2) would live in /etc/nanaimo.cfg, not in the test file.

Right now, /etc/nanaimo.cfg is used to specify the default arguments for fixtures, but the outputs of a fixture cannot be used to parametrize a test or a fixture, [2].

This issue is for a feature that allows pytest parametrization via /etc/nanaimo.cfg (or another fixed, test rig-specific file).