python3: Improve logging, syntax and update deprecated modules to create_manifest

python3: Improve logging, syntax and update deprecated modules to create_manifest

The imp module has een deprecated by upstream python, drop its usage
  (imp.get_tag) in favor of sys.implementation.cache_tag.

Avoid incorrectly getting dependencies for running script and
multiprocessing module.

Improve logging behavior of the create_manifest task:
- Use indentation.
- Logs on temp directory.
- Use a proper debug flag.
- Standarize syntax.

Signed-off-by: Alejandro Enedino Hernandez Samaniego <alejandro@enedino.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>