Use the right raw_config_wrapper configuration file for compose respin.
    
    If we are doing respin of raw_config compose with raw_config_wrapper
    defined, the current code wrongly loads just created empty `main_cfg_path`
    instead the `pungi.conf` which stores the raw_config_wrapper.
    
    Signed-off-by: Jan Kaluza <jkaluza@redhat.com>