Python refactoring and typo error fixes

This PR:

• remove dead code (iotlab_api.py),
• optimize some list / dict / set creation,
• replace logger.warn (deprecated) by logger.warning,
• deprecate symetric parameter in netem.py and htb.py (replace by symmetric, compatibility kept),
• remove two duplicated lines,
• fix import error in enoslib/infra/enos_distem/configuration.py,
• fix some typo errors.