* Parse a directory for *.pem file containing a certificate and private key in PEM format or a single DER cert with subject CNAME as given
*
* @param[in] path directory to parse
* @param[in] subject subject CNAME to look for
* @param[out] certificate result certificate, NULL if not found. Is allocated by this function, caller must do a belle_sip_object_unref on it after use
* @param[out] pkey result private key, NULL if not found. Is allocated by this function, caller must do a belle_sip_object_unref on it after use
* @param[in] format either PEM or DER
* @return 0 if we found a certificate and key matching given subject common name
* @param[in] file_type if not NULL return only the file with the given extension, must include the '.', ex:".pem"
* @return a belle_sip list containing all found file or NULL if no file were found or directory doesn't exist. List must be destroyed using belle_sip_list_free_with_data(<ret_list>, belle_sip_free)