[Libvirt-cim] [PATCH 0 of 5] #2 - Add get_rasd_... functions to RASD and adopt interface changes to assocs

Added get_rasd_by_ref() and get_rasd_by_name() to RASD provider to clean up / fasten the access to a specific RASD instance. This interface change has been adopted by the appropriate associaton providers, who need this access. diff to patch set 1: - fixed get_rasd_by_name and get_rasd_by_ref to only return a valid instance pointer in case of success