[Libvirt-cim] [PATCH 0 of 3] #2 - Add configurable enum_devices() to Device provider and Adopt interface changes to SD & EAFP

This patch set implements the configurable enum_devices() interface to the Device provider. This slight interface change is adopted to the associations SystemDevice and ElementAllocatedFromPool. Both associations profit from the easy access to the device instances. Diff to patch set 1: - fixed style issues