Ensure DiAbstractServiceFactory takes lowest possible priority

I'm far from expert on all the intricacies of Zend\Di, but this
*seemed* necessary for my application.

AFAICT, the `Zend\ServiceManager\Di\DiAbstractServiceFactory`
will be lazily added to the shared ServiceManager at an unpredictable
time. The default behaviour of `addAbstractFactory` puts this new
abstract factory in front of abstract factories from modules, which leads
to the DiAbstractFactory trying to create things before module-defined
abstract factories get a chance.