Fix TestingAccessWrapper private property access and parent classes

Fix TestingAccessWrapper private property access and parent classes

PHP's reflection mechanism is weird: reflecting on a private method will
find it even if it's defined in a parent class, while reflecting on a
private property just fails.

It would likely be more useful if TestingAccessWrapper could find
private properties defined in parent classes, so let's make that happen.

Change-Id: I9cfdde2694136d0e4559cc419a528762ea14ae4b