SPARK-3331 [BUILD] PEP8 tests fail because they check unzipped py4j code

PEP8 tests run on files under "./python", but unzipped py4j code is found at "./python/build/py4j". Py4J code fails style checks and can fail ./dev/run-tests if this code is present locally.

Author: Sean Owen <sowen@cloudera.com>

Closes #2222 from srowen/SPARK-3331 and squashes the following commits:

34711ec [Sean Owen] Restrict lint check to pyspark/, since the local directory can contain unzipped py4j code in build/py4j
[SPARK-3061] Fix Maven build under Windows

The Maven build was failing on Windows because it tried to call the unix `unzip` utility to extract the Py4J files into core's build directory.  I've fixed this issue by using the `maven-antrun-plugin` to perform the unzipping.

I also fixed an issue that prevented tests from running under Windows:

In the Maven ScalaTest plugin, the filename listed in <filereports> is placed under the <reportsDirectory>; the current code places it in a subdirectory of reportsDirectory, e.g.

```
${project.build.directory}/surefire-reports/${project.build.directory}/SparkTestSuite.txt
```

This caused problems under Windows because it would try to create a subdirectory named "c:\\".

Note that the tests still fail under Windows (for other reasons); this PR just allows them to run and fail rather than crash when trying to create the test reports directory.

Author: Josh Rosen <joshrosen@apache.org>
Author: Josh Rosen <rosenville@gmail.com>
Author: Josh Rosen <joshrosen@databricks.com>

Closes #2165 from JoshRosen/windows-support and squashes the following commits:

651d210 [Josh Rosen] Unzip to python/build instead of core/build
fbf3e61 [Josh Rosen] 4 spaces -> 2 spaces
e347668 [Josh Rosen] Fix Maven scalatest filereports path:
4994af1 [Josh Rosen] [SPARK-3061] Use maven-antrun-plugin to unzip Py4J.
[SPARK-1919] Fix Windows spark-shell --jars

We were trying to add `file:/C:/path/to/my.jar` to the class path. We should add `C:/path/to/my.jar` instead. Tested on Windows 8.1.

Author: Andrew Or <andrewor14@gmail.com>

Closes #2211 from andrewor14/windows-shell-jars and squashes the following commits:

262c6a2 [Andrew Or] Oops... Add the new code to the correct place
0d5a0c1 [Andrew Or] Format jar path only for adding to shell classpath
42bd626 [Andrew Or] Remove unnecessary code
0049f1b [Andrew Or] Remove embarrassing log messages
b1755a0 [Andrew Or] Format jar paths properly before adding them to the classpath
[SPARK-3347] [yarn] Fix yarn-alpha compilation.

Missing import. Oops.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #2236 from vanzin/SPARK-3347 and squashes the following commits:

594fc39 [Marcelo Vanzin] [SPARK-3347] [yarn] Fix yarn-alpha compilation.
SPARK-3052. Misleading and spurious FileSystem closed errors whenever a ...

...job fails while reading from Hadoop

Author: Sandy Ryza <sandy@cloudera.com>

Closes #1956 from sryza/sandy-spark-3052 and squashes the following commits:

815813a [Sandy Ryza] SPARK-3052. Misleading and spurious FileSystem closed errors whenever a job fails while reading from Hadoop
[SPARK-2871] [PySpark] add countApproxDistinct() API

RDD.countApproxDistinct(relativeSD=0.05):

        :: Experimental ::
        Return approximate number of distinct elements in the RDD.

        The algorithm used is based on streamlib's implementation of
        "HyperLogLog in Practice: Algorithmic Engineering of a State
        of The Art Cardinality Estimation Algorithm", available
        <a href="http://dx.doi.org/10.1145/2452376.2452456">here</a>.

        This support all the types of objects, which is supported by
        Pyrolite, nearly all builtin types.

        param relativeSD Relative accuracy. Smaller values create
                           counters that require more space.
                           It must be greater than 0.000017.

        >>> n = sc.parallelize(range(1000)).map(str).countApproxDistinct()
        >>> 950 < n < 1050
        True
        >>> n = sc.parallelize([i % 20 for i in range(1000)]).countApproxDistinct()
        >>> 18 < n < 22
        True

Author: Davies Liu <davies.liu@gmail.com>

Closes #2142 from davies/countApproxDistinct and squashes the following commits:

e20da47 [Davies Liu] remove the correction in Python
c38c4e4 [Davies Liu] fix doc tests
2ab157c [Davies Liu] fix doc tests
9d2565f [Davies Liu] add commments and link for hash collision correction
d306492 [Davies Liu] change range of hash of tuple to [0, maxint]
ded624f [Davies Liu] calculate hash in Python
4cba98f [Davies Liu] add more tests
a85a8c6 [Davies Liu] Merge branch 'master' into countApproxDistinct
e97e342 [Davies Liu] add countApproxDistinct()