[SPARK-2627] [PySpark] have the build enforce PEP 8 automatically

As described in [SPARK-2627](https://issues.apache.org/jira/browse/SPARK-2627), we'd like Python code to automatically be checked for PEP 8 compliance by Jenkins. This pull request aims to do that.

Notes:
* We may need to install [`pep8`](https://pypi.python.org/pypi/pep8) on the build server.
* I'm expecting tests to fail now that PEP 8 compliance is being checked as part of the build. I'm fine with cleaning up any remaining PEP 8 violations as part of this pull request.
* I did not understand why the RAT and scalastyle reports are saved to text files. I did the same for the PEP 8 check, but only so that the console output style can match those for the RAT and scalastyle checks. The PEP 8 report is removed right after the check is complete.
* Updates to the ["Contributing to Spark"](https://cwiki.apache.org/confluence/display/SPARK/Contributing+to+Spark) guide will be submitted elsewhere, as I don't believe that text is part of the Spark repo.

Author: Nicholas Chammas <nicholas.chammas@gmail.com>
Author: nchammas <nicholas.chammas@gmail.com>

Closes #1744 from nchammas/master and squashes the following commits:

274b238 [Nicholas Chammas] [SPARK-2627] [PySpark] minor indentation changes
983d963 [nchammas] Merge pull request #5 from apache/master
1db5314 [nchammas] Merge pull request #4 from apache/master
0e0245f [Nicholas Chammas] [SPARK-2627] undo erroneous whitespace fixes
bf30942 [Nicholas Chammas] [SPARK-2627] PEP8: comment spacing
6db9a44 [nchammas] Merge pull request #3 from apache/master
7b4750e [Nicholas Chammas] merge upstream changes
91b7584 [Nicholas Chammas] [SPARK-2627] undo unnecessary line breaks
44e3e56 [Nicholas Chammas] [SPARK-2627] use tox.ini to exclude files
b09fae2 [Nicholas Chammas] don't wrap comments unnecessarily
bfb9f9f [Nicholas Chammas] [SPARK-2627] keep up with the PEP 8 fixes
9da347f [nchammas] Merge pull request #2 from apache/master
aa5b4b5 [Nicholas Chammas] [SPARK-2627] follow Spark bash style for if blocks
d0a83b9 [Nicholas Chammas] [SPARK-2627] check that pep8 downloaded fine
dffb5dd [Nicholas Chammas] [SPARK-2627] download pep8 at runtime
a1ce7ae [Nicholas Chammas] [SPARK-2627] space out test report sections
21da538 [Nicholas Chammas] [SPARK-2627] it's PEP 8, not PEP8
6f4900b [Nicholas Chammas] [SPARK-2627] more misc PEP 8 fixes
fe57ed0 [Nicholas Chammas] removing merge conflict backups
9c01d4c [nchammas] Merge pull request #1 from apache/master
9a66cb0 [Nicholas Chammas] resolving merge conflicts
a31ccc4 [Nicholas Chammas] [SPARK-2627] miscellaneous PEP 8 fixes
beaa9ac [Nicholas Chammas] [SPARK-2627] fail check on non-zero status
723ed39 [Nicholas Chammas] always delete the report file
0541ebb [Nicholas Chammas] [SPARK-2627] call Python linter from run-tests
12440fa [Nicholas Chammas] [SPARK-2627] add Scala linter
61c07b9 [Nicholas Chammas] [SPARK-2627] add Python linter
75ad552 [Nicholas Chammas] make check output style consistent

1 files changed, 7 insertions, 4 deletions

diff --git a/python/pyspark/mllib/tests.py b/python/pyspark/mllib/tests.py
index 9d1e5be637..6f3ec8ac94 100644
--- a/python/pyspark/mllib/tests.py
+++ b/python/pyspark/mllib/tests.py
@@ -39,6 +39,7 @@ except:
 
 
 class VectorTests(unittest.TestCase):
+
     def test_serialize(self):
         sv = SparseVector(4, {1: 1, 3: 2})
         dv = array([1., 2., 3., 4.])
@@ -81,6 +82,7 @@ class VectorTests(unittest.TestCase):
 
 
 class ListTests(PySparkTestCase):
+
     """
     Test MLlib algorithms on plain lists, to make sure they're passed through
     as NumPy arrays.
@@ -128,7 +130,7 @@ class ListTests(PySparkTestCase):
         self.assertTrue(nb_model.predict(features[2]) <= 0)
         self.assertTrue(nb_model.predict(features[3]) > 0)
 
-        categoricalFeaturesInfo = {0: 3} # feature 0 has 3 categories
+        categoricalFeaturesInfo = {0: 3}  # feature 0 has 3 categories
         dt_model = \
             DecisionTree.trainClassifier(rdd, numClasses=2,
                                          categoricalFeaturesInfo=categoricalFeaturesInfo)
@@ -168,7 +170,7 @@ class ListTests(PySparkTestCase):
         self.assertTrue(rr_model.predict(features[2]) <= 0)
         self.assertTrue(rr_model.predict(features[3]) > 0)
 
-        categoricalFeaturesInfo = {0: 2} # feature 0 has 2 categories
+        categoricalFeaturesInfo = {0: 2}  # feature 0 has 2 categories
         dt_model = \
             DecisionTree.trainRegressor(rdd, categoricalFeaturesInfo=categoricalFeaturesInfo)
         self.assertTrue(dt_model.predict(features[0]) <= 0)
@@ -179,6 +181,7 @@ class ListTests(PySparkTestCase):
 
 @unittest.skipIf(not _have_scipy, "SciPy not installed")
 class SciPyTests(PySparkTestCase):
+
     """
     Test both vector operations and MLlib algorithms with SciPy sparse matrices,
     if SciPy is available.
@@ -276,7 +279,7 @@ class SciPyTests(PySparkTestCase):
         self.assertTrue(nb_model.predict(features[2]) <= 0)
         self.assertTrue(nb_model.predict(features[3]) > 0)
 
-        categoricalFeaturesInfo = {0: 3} # feature 0 has 3 categories
+        categoricalFeaturesInfo = {0: 3}  # feature 0 has 3 categories
         dt_model = DecisionTree.trainClassifier(rdd, numClasses=2,
                                                 categoricalFeaturesInfo=categoricalFeaturesInfo)
         self.assertTrue(dt_model.predict(features[0]) <= 0)
@@ -315,7 +318,7 @@ class SciPyTests(PySparkTestCase):
         self.assertTrue(rr_model.predict(features[2]) <= 0)
         self.assertTrue(rr_model.predict(features[3]) > 0)
 
-        categoricalFeaturesInfo = {0: 2} # feature 0 has 2 categories
+        categoricalFeaturesInfo = {0: 2}  # feature 0 has 2 categories
         dt_model = DecisionTree.trainRegressor(rdd, categoricalFeaturesInfo=categoricalFeaturesInfo)
         self.assertTrue(dt_model.predict(features[0]) <= 0)
         self.assertTrue(dt_model.predict(features[1]) > 0)