[SPARK-13583][CORE][STREAMING] Remove unused imports and add checkstyle rule

## What changes were proposed in this pull request?

After SPARK-6990, `dev/lint-java` keeps Java code healthy and helps PR review by saving much time.
This issue aims remove unused imports from Java/Scala code and add `UnusedImports` checkstyle rule to help developers.

## How was this patch tested?
```
./dev/lint-java
./build/sbt compile
```

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11438 from dongjoon-hyun/SPARK-13583.

6 files changed, 6 insertions, 12 deletions

diff --git a/yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMasterArguments.scala b/yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMasterArguments.scala
index 87f50875e3..6987e5a55f 100644
--- a/yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMasterArguments.scala
+++ b/yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMasterArguments.scala
@@ -19,7 +19,6 @@ package org.apache.spark.deploy.yarn
 
 import scala.collection.mutable.ArrayBuffer
 
-import org.apache.spark.deploy.yarn.YarnSparkHadoopUtil._
 import org.apache.spark.util.{IntParam, MemoryParam}
 
 class ApplicationMasterArguments(val args: Array[String]) {
diff --git a/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala b/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala
index dac3ea2517..be45e9597f 100644
--- a/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala
+++ b/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala
@@ -19,15 +19,13 @@ package org.apache.spark.deploy.yarn
 
 import java.io.{ByteArrayInputStream, DataInputStream, File, FileOutputStream, IOException,
   OutputStreamWriter}
-import java.net.{InetAddress, UnknownHostException, URI, URISyntaxException}
+import java.net.{InetAddress, UnknownHostException, URI}
 import java.nio.ByteBuffer
-import java.security.PrivilegedExceptionAction
 import java.util.{Properties, UUID}
 import java.util.zip.{ZipEntry, ZipOutputStream}
 
 import scala.collection.JavaConverters._
 import scala.collection.mutable.{ArrayBuffer, HashMap, HashSet, ListBuffer, Map}
-import scala.reflect.runtime.universe
 import scala.util.{Failure, Success, Try}
 import scala.util.control.NonFatal
 
@@ -38,10 +36,9 @@ import org.apache.hadoop.conf.Configuration
 import org.apache.hadoop.fs._
 import org.apache.hadoop.fs.permission.FsPermission
 import org.apache.hadoop.hdfs.security.token.delegation.DelegationTokenIdentifier
-import org.apache.hadoop.io.{DataOutputBuffer, Text}
+import org.apache.hadoop.io.DataOutputBuffer
 import org.apache.hadoop.mapreduce.MRJobConfig
 import org.apache.hadoop.security.{Credentials, UserGroupInformation}
-import org.apache.hadoop.security.token.{Token, TokenIdentifier}
 import org.apache.hadoop.util.StringUtils
 import org.apache.hadoop.yarn.api._
 import org.apache.hadoop.yarn.api.ApplicationConstants.Environment
diff --git a/yarn/src/main/scala/org/apache/spark/deploy/yarn/YarnRMClient.scala b/yarn/src/main/scala/org/apache/spark/deploy/yarn/YarnRMClient.scala
index af83cf6a77..98505b93dd 100644
--- a/yarn/src/main/scala/org/apache/spark/deploy/yarn/YarnRMClient.scala
+++ b/yarn/src/main/scala/org/apache/spark/deploy/yarn/YarnRMClient.scala
@@ -19,8 +19,8 @@ package org.apache.spark.deploy.yarn
 
 import java.util.{List => JList}
 
-import scala.collection.{Map, Set}
 import scala.collection.JavaConverters._
+import scala.collection.Map
 import scala.util.Try
 
 import org.apache.hadoop.conf.Configuration
@@ -32,7 +32,6 @@ import org.apache.hadoop.yarn.webapp.util.WebAppUtils
 
 import org.apache.spark.{Logging, SecurityManager, SparkConf}
 import org.apache.spark.rpc.RpcEndpointRef
-import org.apache.spark.scheduler.SplitInfo
 import org.apache.spark.util.Utils
 
 /**
diff --git a/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManagerSuite.scala b/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManagerSuite.scala
index 4cffbb2e9b..ac8f663df2 100644
--- a/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManagerSuite.scala
+++ b/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManagerSuite.scala
@@ -26,11 +26,10 @@ import org.apache.hadoop.conf.Configuration
 import org.apache.hadoop.fs.FileStatus
 import org.apache.hadoop.fs.FileSystem
 import org.apache.hadoop.fs.Path
-import org.apache.hadoop.fs.permission.FsAction
 import org.apache.hadoop.yarn.api.records.LocalResource
 import org.apache.hadoop.yarn.api.records.LocalResourceType
 import org.apache.hadoop.yarn.api.records.LocalResourceVisibility
-import org.apache.hadoop.yarn.util.{ConverterUtils, Records}
+import org.apache.hadoop.yarn.util.ConverterUtils
 import org.mockito.Mockito.when
 import org.scalatest.mock.MockitoSugar
 
diff --git a/yarn/src/test/scala/org/apache/spark/deploy/yarn/YarnClusterSuite.scala b/yarn/src/test/scala/org/apache/spark/deploy/yarn/YarnClusterSuite.scala
index 60d35d3452..e935163c34 100644
--- a/yarn/src/test/scala/org/apache/spark/deploy/yarn/YarnClusterSuite.scala
+++ b/yarn/src/test/scala/org/apache/spark/deploy/yarn/YarnClusterSuite.scala
@@ -19,7 +19,7 @@ package org.apache.spark.deploy.yarn
 
 import java.io.File
 import java.net.URL
-import java.util.{HashMap => JHashMap, Properties}
+import java.util.{HashMap => JHashMap}
 
 import scala.collection.mutable
 import scala.concurrent.duration._
diff --git a/yarn/src/test/scala/org/apache/spark/network/shuffle/ShuffleTestAccessor.scala b/yarn/src/test/scala/org/apache/spark/network/shuffle/ShuffleTestAccessor.scala
index d6902c7bb0..1fed2562fc 100644
--- a/yarn/src/test/scala/org/apache/spark/network/shuffle/ShuffleTestAccessor.scala
+++ b/yarn/src/test/scala/org/apache/spark/network/shuffle/ShuffleTestAccessor.scala
@@ -16,7 +16,7 @@
  */
 package org.apache.spark.network.shuffle
 
-import java.io.{File, IOException}
+import java.io.File
 import java.util.concurrent.ConcurrentMap
 
 import org.apache.hadoop.yarn.api.records.ApplicationId