[SPARK-2627] add Python linter

This guy just runs the pep8 utility on all code in the python
directory, minus cloudpickle, which is a 3rd-party library.

dev/lint-python

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+SCRIPT_DIR="$( cd "$( dirname "$0" )" && pwd )"
+SPARK_ROOT_DIR="$(dirname $SCRIPT_DIR)"
+PEP8_REPORT_PATH="$SPARK_ROOT_DIR/dev/pep8-report.txt"
+
+cd $SPARK_ROOT_DIR
+# There is no need to write this output to a file
+#+ first, but we do so so that the check status can
+#+ be output before the report, like with the
+#+ scalastyle and RAT checks.
+pep8 ./python --exclude="cloudpickle.py" \
+    > "$PEP8_REPORT_PATH"
+pep8_status=${PIPESTATUS[0]} #$?
+
+if [ $pep8_status ]
+    then
+        echo "PEP8 checks failed."
+        cat "$PEP8_REPORT_PATH"
+        exit 1
+    else
+        echo "PEP8 checks passed."
+fi
+
+rm -f "$PEP8_REPORT_PATH"