WIP: Improved python3 compatibility and applied flake8 fixes.

For python3 compatibility replaced:

• print by print function from future or by python logger to improve python3 compatibility,
• except [class], [var]: by except [class] as [var]:,
• raise [class],[msg] by raise class,
• octal mumbers e.g. 0755 by 0o755,
• commands.getstatusoutput by subprocess based solution.

To fix flake8 warnings, replaced

• membership test: not [val] in [dict] by [val] not in [dict],
• ==None by is None and !=None by not is None,
• renamed ambiguous variables.