[SPARK-14868][BUILD] Enable NewLineAtEofChecker in checkstyle and fix lint-java errors

## What changes were proposed in this pull request?

Spark uses `NewLineAtEofChecker` rule in Scala by ScalaStyle. And, most Java code also comply with the rule. This PR aims to enforce the same rule `NewlineAtEndOfFile` by CheckStyle explicitly. Also, this fixes lint-java errors since SPARK-14465. The followings are the items.

- Adds a new line at the end of the files (19 files)
- Fixes 25 lint-java errors (12 RedundantModifier, 6 **ArrayTypeStyle**, 2 LineLength, 2 UnusedImports, 2 RegexpSingleline, 1 ModifierOrder)

## How was this patch tested?

After the Jenkins test succeeds, `dev/lint-java` should pass. (Currently, Jenkins dose not run lint-java.)
```bash
$ dev/lint-java
Using `mvn` from path: /usr/local/bin/mvn
Checkstyle checks passed.
```

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12632 from dongjoon-hyun/SPARK-14868.

1 files changed, 1 insertions, 1 deletions

diff --git a/external/flume/src/main/scala/org/apache/spark/streaming/flume/package-info.java b/external/flume/src/main/scala/org/apache/spark/streaming/flume/package-info.java
index d31aa5f5c0..4a5da226ad 100644
--- a/external/flume/src/main/scala/org/apache/spark/streaming/flume/package-info.java
+++ b/external/flume/src/main/scala/org/apache/spark/streaming/flume/package-info.java
@@ -18,4 +18,4 @@
 /**
  * Spark streaming receiver for Flume.
  */
-package org.apache.spark.streaming.flume;
\ No newline at end of file
+package org.apache.spark.streaming.flume;