Support regenerating raw_config composes using the stored pungi_config_dump.
    
    This commit also changes the input to Pungi from classic pungi.conf
    to pungi.json for all composes to keep the code consistent.
    
    This is needed, because there is no reliable way to convert
    pungi_config_dump from JSON to PyConfigParser format. Using JSON
    instead for all Pungi configuration files passes to Pungi seems
    to be a better option.