MAPREDUCE-7281. Fix NoClassDefFoundError on 'mapred minicluster'. (#2077)

(cherry picked from commit 8fd0fdf8890b4c0cf3ea977be8fae8fa17e6599b)

hadoop-mapreduce-project/bin/mapred

@@ -105,6 +105,8 @@ function mapredcmd_case
     minicluster)
       hadoop_add_classpath "${HADOOP_YARN_HOME}/${YARN_DIR}/timelineservice"'/*'
       hadoop_add_classpath "${HADOOP_YARN_HOME}/${YARN_DIR}/test"'/*'
+      junitjar=$(echo "${HADOOP_TOOLS_LIB_JARS_DIR}"/junit-[0-9]*.jar)
+      hadoop_add_classpath "${junitjar}"
       HADOOP_CLASSNAME=org.apache.hadoop.mapreduce.MiniHadoopClusterManager
     ;;
     *)