[SPARK-11731][STREAMING] Enable batching on Driver WriteAheadLog by default

[brkyvz]

Using batching on the driver for the WriteAheadLog should be an improvement for all environments and use cases. Users will be able to scale to much higher number of receivers with the BatchedWriteAheadLog. Therefore we should turn it on by default, and QA it in the QA period.

I've also added some tests to make sure the default configurations are correct regarding recent additions:

• batching on by default
• closeFileAfterWrite off by default
• parallelRecovery off by default

[SparkQA]

Test build #45872 has finished for PR 9695 at commit dfe29b8.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * public class JavaGradientBoostingClassificationExample\n * public class JavaGradientBoostingRegressionExample\n * public class JavaRandomForestClassificationExample\n * public class JavaRandomForestRegressionExample\n

[SparkQA]

Test build #45876 has finished for PR 9695 at commit 2cbf59e.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[brkyvz]

retest this please

[SparkQA]

Test build #45884 has finished for PR 9695 at commit 2cbf59e.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[zsxwing]

LGTM

[harishreedharan]

+1

[tdas]

LGTM. Merging this to master and 1.6