Make s_all accept Python PEP8 compliant line breaks

The WiredTiger s_all script incorrectly generates errors (ie false positives) when checking the whitespace (in particular the usage of blank lines) in Python files that follow the industry-wide coding standard for Python (PEP8).

PEP8 specifies "Surround top-level function and class definitions with two blank lines.".

If a file contain 2 blank lines, where required by the PEP8 standard, the s_all script rejects that saying that one line is required. This creates a false positive error.

Definition of done:

• s_all accepts, without error, Python code that follows the PEP8 standard for blank lines