- Move external/java8-tests tests into core, streaming, sql and remove
- Remove MaxPermGen and related options
- Fix some reflection / TODOs around Java 8+ methods
- Update doc references to 1.7/1.8 differences
- Remove Java 7/8 related build profiles
- Update some plugins for better Java 8 compatibility
- Fix a few Java-related warnings

For the future:

- Update Java 8 examples to fully use Java 8
- Update Java tests to use lambdas for simplicity
- Update Java internal implementations to use lambdas

## How was this patch tested?

Existing tests

Author: Sean Owen <sowen@cloudera.com>

Closes #16871 from srowen/SPARK-19493.

## What changes were proposed in this pull request?

It seems wintuils for Hadoop 2.6.5 not exiting for now in https://github.com/steveloughran/winutils

This breaks the tests in SparkR on Windows so this PR proposes to use winutils built by Hadoop 2.6.4 for now.

## How was this patch tested?

Manually via AppVeyor

**Before**

https://ci.appveyor.com/project/spark-test/spark/build/627-r-test-break

**After**

https://ci.appveyor.com/project/spark-test/spark/build/629-r-test-break

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #16927 from HyukjinKwon/spark-r-windows-break.

## What changes were proposed in this pull request?

- Remove support for Hadoop 2.5 and earlier
- Remove reflection and code constructs only needed to support multiple versions at once
- Update docs to reflect newer versions
- Remove older versions' builds and profiles.

## How was this patch tested?

Existing tests

Author: Sean Owen <sowen@cloudera.com>

Closes #16810 from srowen/SPARK-19464.

[SPARK-19221][PROJECT INFRA][R] Add winutils binaries to the path in AppVeyor tests for Hadoop libraries to call native codes properly

## What changes were proposed in this pull request?

It seems Hadoop libraries need winutils binaries for native libraries in the path.

It is not a problem in tests for now because we are only testing SparkR on Windows via AppVeyor but it can be a problem if we run Scala tests via AppVeyor as below:

```
 - SPARK-18220: read Hive orc table with varchar column *** FAILED *** (3 seconds, 937 milliseconds)
   org.apache.spark.sql.execution.QueryExecutionException: FAILED: Execution Error, return code -101 from org.apache.hadoop.hive.ql.exec.mr.MapRedTask. org.apache.hadoop.io.nativeio.NativeIO$Windows.access0(Ljava/lang/String;I)Z
   at org.apache.spark.sql.hive.client.HiveClientImpl$$anonfun$runHive$1.apply(HiveClientImpl.scala:625)
   at org.apache.spark.sql.hive.client.HiveClientImpl$$anonfun$runHive$1.apply(HiveClientImpl.scala:609)
   at org.apache.spark.sql.hive.client.HiveClientImpl$$anonfun$withHiveState$1.apply(HiveClientImpl.scala:283)
   ...
```

This PR proposes to add it to the `Path` for AppVeyor tests.

## How was this patch tested?

Manually via AppVeyor.

**Before**
https://ci.appveyor.com/project/spark-test/spark/build/549-windows-complete/job/gc8a1pjua2bc4i8m

**After**
https://ci.appveyor.com/project/spark-test/spark/build/572-windows-complete/job/c4vrysr5uvj2hgu7

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #16584 from HyukjinKwon/set-path-appveyor.

[SPARK-17200][PROJECT INFRA][BUILD][SPARKR] Automate building and testing on Windows (currently SparkR only)

## What changes were proposed in this pull request?

This PR adds the build automation on Windows with [AppVeyor](https://www.appveyor.com/) CI tool.

Currently, this only runs the tests for SparkR as we have been having some issues with testing Windows-specific PRs (e.g. https://github.com/apache/spark/pull/14743 and https://github.com/apache/spark/pull/13165) and hard time to verify this.

One concern is, this build is dependent on [steveloughran/winutils](https://github.com/steveloughran/winutils) for pre-built Hadoop bin package (who is a Hadoop PMC member).

## How was this patch tested?

Manually, https://ci.appveyor.com/project/HyukjinKwon/spark/build/88-SPARK-17200-build-profile
This takes roughly 40 mins.

Some tests are already being failed and this was found in https://github.com/apache/spark/pull/14743#issuecomment-241405287.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #14859 from HyukjinKwon/SPARK-17200-build.