smooth-dl.py: fix some pylint issues

smooth-dl.py: fix some pylint issues

  C: 59, 0: Unnecessary parens after 'assert' keyword (superfluous-parens)
  W: 67, 0: Bad indentation. Found 12 spaces, expected 8 (bad-indentation)
  C:232, 0: Exactly one space required after comma
          chunk_file = os.path.join(dest_dir,  chunks_quality, chunk_name)
                                            ^ (bad-whitespace)
  W:341, 0: Bad indentation. Found 8 spaces, expected 4 (bad-indentation)
  W:342, 0: Bad indentation. Found 12 spaces, expected 8 (bad-indentation)
  W:344, 0: Bad indentation. Found 8 spaces, expected 4 (bad-indentation)
  W:345, 0: Bad indentation. Found 12 spaces, expected 8 (bad-indentation)
  W:347, 0: Bad indentation. Found 12 spaces, expected 8 (bad-indentation)
  W:350, 0: Bad indentation. Found 8 spaces, expected 4 (bad-indentation)
  W:351, 0: Bad indentation. Found 8 spaces, expected 4 (bad-indentation)
  W:353, 0: Bad indentation. Found 8 spaces, expected 4 (bad-indentation)
  W:355, 0: Bad indentation. Found 8 spaces, expected 4 (bad-indentation)
  W:360, 0: Bad indentation. Found 8 spaces, expected 4 (bad-indentation)
  W:365, 0: Bad indentation. Found 8 spaces, expected 4 (bad-indentation)
  W:370, 0: Bad indentation. Found 8 spaces, expected 4 (bad-indentation)
  C:396, 0: Exactly one space required after comma
      parser.add_option("-v", "--video-stream",  metavar="<n>",
                                              ^ (bad-whitespace)
  C: 43, 0: Invalid constant name "__description" (invalid-name)
  C: 44, 0: Invalid constant name "__version" (invalid-name)
  C: 45, 0: Invalid constant name "__author_info" (invalid-name)
  W:100,32: Unused variable 'e' (unused-variable)
  W:112,17: Redefining name 'url' from outer scope (line 421) (redefined-outer-name)
  W:130, 4: Redefining name 'manifest' from outer scope (line 422) (redefined-outer-name)
  C:115, 7: Comparison to False should be 'not expr' or 'expr is False' (singleton-comparison)
  W:150,24: Redefining name 'manifest' from outer scope (line 422) (redefined-outer-name)
  W:156, 8: Redefining name 'url' from outer scope (line 421) (redefined-outer-name)
  W:156, 8: Unused variable 'url' (unused-variable)
  W:194, 4: Redefining name 'url' from outer scope (line 421) (redefined-outer-name)
  W:205, 4: Redefining name 'url' from outer scope (line 421) (redefined-outer-name)
  W:211,30: Redefining name 'manifest' from outer scope (line 422) (redefined-outer-name)
  C:213, 7: Comparison to False should be 'not expr' or 'expr is False' (singleton-comparison)
  C:221, 7: Comparison to False should be 'not expr' or 'expr is False' (singleton-comparison)
  C:234,11: Comparison to False should be 'not expr' or 'expr is False' (singleton-comparison)
  W:248,19: Redefining name 'manifest' from outer scope (line 422) (redefined-outer-name)
  W:306,22: Redefining name 'manifest' from outer scope (line 422) (redefined-outer-name)
  W:328,22: Redefining name 'manifest' from outer scope (line 422) (redefined-outer-name)
  W:335,20: Redefining name 'url' from outer scope (line 421) (redefined-outer-name)
  W:335,25: Redefining name 'manifest' from outer scope (line 422) (redefined-outer-name)
  W:376, 4: Redefining name 'parser' from outer scope (line 414) (redefined-outer-name)
  C:414, 4: Invalid constant name "parser" (invalid-name)
  C:415, 5: Invalid constant name "options" (invalid-name)
  C:415,14: Invalid constant name "args" (invalid-name)
  C:421, 4: Invalid constant name "url" (invalid-name)
  C:422, 4: Invalid constant name "manifest" (invalid-name)
  C:422,14: Invalid constant name "url" (invalid-name)