[SPARK-15031][EXAMPLE] Use SparkSession in Scala/Python/Java example.

## What changes were proposed in this pull request?

This PR aims to update Scala/Python/Java examples by replacing `SQLContext` with newly added `SparkSession`.

- Use **SparkSession Builder Pattern** in 154(Scala 55, Java 52, Python 47) files.
- Add `getConf` in Python SparkContext class: `python/pyspark/context.py`
- Replace **SQLContext Singleton Pattern** with **SparkSession Singleton Pattern**:
  - `SqlNetworkWordCount.scala`
  - `JavaSqlNetworkWordCount.java`
  - `sql_network_wordcount.py`

Now, `SQLContexts` are used only in R examples and the following two Python examples. The python examples are untouched in this PR since it already fails some unknown issue.
- `simple_params_example.py`
- `aft_survival_regression.py`

## How was this patch tested?

Manual.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12809 from dongjoon-hyun/SPARK-15031.

1 files changed, 4 insertions, 2 deletions

diff --git a/examples/src/main/python/mllib/binary_classification_metrics_example.py b/examples/src/main/python/mllib/binary_classification_metrics_example.py
index 4e7ea289b2..8f0fc9d45d 100644
--- a/examples/src/main/python/mllib/binary_classification_metrics_example.py
+++ b/examples/src/main/python/mllib/binary_classification_metrics_example.py
@@ -18,7 +18,7 @@
 Binary Classification Metrics Example.
 """
 from __future__ import print_function
-from pyspark import SparkContext, SQLContext
+from pyspark import SparkContext
 # $example on$
 from pyspark.mllib.classification import LogisticRegressionWithLBFGS
 from pyspark.mllib.evaluation import BinaryClassificationMetrics
@@ -27,7 +27,7 @@ from pyspark.mllib.util import MLUtils
 
 if __name__ == "__main__":
     sc = SparkContext(appName="BinaryClassificationMetricsExample")
-    sqlContext = SQLContext(sc)
+
     # $example on$
     # Several of the methods available in scala are currently missing from pyspark
     # Load training data in LIBSVM format
@@ -52,3 +52,5 @@ if __name__ == "__main__":
     # Area under ROC curve
     print("Area under ROC = %s" % metrics.areaUnderROC)
     # $example off$
+
+    sc.stop()