Refactor/rewrite nodejs.prov
    
    Adjust the nodejs.prov script to be more pythonic and easier to modify
    downstream (i.e. SCLs).
    
    - Remove global state
    - Better function separation (metadata formatting/metadata retrieval)
    - Replace ad-hoc directory traversal with os.walk()
    - Extract bits usually modified downstream into module-level "constants"
    
    Signed-off-by: Jan Staněk <jstanek@redhat.com>