[SPARK-8483] [STREAMING] Remove commons-lang3 dependency from Flume Si…

…nk. Also bump Flume version to 1.6.0

Author: Hari Shreedharan <hshreedharan@apache.org>

Closes #6910 from harishreedharan/remove-commons-lang3 and squashes the following commits:

9875f7d [Hari Shreedharan] Revert back to Flume 1.4.0
ca35eb0 [Hari Shreedharan] [SPARK-8483][Streaming] Remove commons-lang3 dependency from Flume Sink. Also bump Flume version to 1.6.0

external/flume-sink/pom.xml

@@ -35,10 +35,6 @@
   <url>http://spark.apache.org/</url>
 
   <dependencies>
-    <dependency>
-      <groupId>org.apache.commons</groupId>
-      <artifactId>commons-lang3</artifactId>
-    </dependency>
     <dependency>
       <groupId>org.apache.flume</groupId>
       <artifactId>flume-ng-sdk</artifactId>

external/flume-sink/src/main/scala/org/apache/spark/streaming/flume/sink/SparkAvroCallbackHandler.scala

@@ -16,13 +16,13 @@
  */
 package org.apache.spark.streaming.flume.sink
 
+import java.util.UUID
 import java.util.concurrent.{CountDownLatch, Executors}
 import java.util.concurrent.atomic.AtomicLong
 
 import scala.collection.mutable
 
 import org.apache.flume.Channel
-import org.apache.commons.lang3.RandomStringUtils
 
 /**
  * Class that implements the SparkFlumeProtocol, that is used by the Avro Netty Server to process
@@ -53,7 +53,7 @@ private[flume] class SparkAvroCallbackHandler(val threads: Int, val channel: Cha
   // Since the new txn may not have the same sequence number we must guard against accidentally
   // committing a new transaction. To reduce the probability of that happening a random string is
   // prepended to the sequence number. Does not change for life of sink
-  private val seqBase = RandomStringUtils.randomAlphanumeric(8)
+  private val seqBase = UUID.randomUUID().toString.substring(0, 8)
   private val seqCounter = new AtomicLong(0)
 
   // Protected by `sequenceNumberToProcessor`