[SPARK-2627] use tox.ini to exclude files

No need to exclude files in the call to pep8. The tool references
tox.ini for config information, so we should use that.

Author: nchammas

dev/lint-python

@@ -44,8 +44,7 @@ fi
 #+ first, but we do so so that the check status can
 #+ be output before the report, like with the
 #+ scalastyle and RAT checks.
-python $PEP8_SCRIPT_PATH ./python --exclude="cloudpickle.py" \
-    > "$PEP8_REPORT_PATH"
+python $PEP8_SCRIPT_PATH ./python > "$PEP8_REPORT_PATH"
 pep8_status=${PIPESTATUS[0]} #$?
 
 if [ $pep8_status -ne 0 ]; then

tox.ini

@@ -15,3 +15,4 @@
 
 [pep8]
 max-line-length=100
+exclude=cloudpickle.py