[ZEPPELIN-4962]. Support for manually specifying the Java version of Spark Interpreter Scala REPL and fix the CI failure due to low Scala version

docs/interpreter/spark.md

@@ -195,10 +195,21 @@ You can also set other Spark properties which are not listed in the table. For a
       (ex: http://{{PORT}}-{{SERVICE_NAME}}.{{SERVICE_DOMAIN}})
      </td>
   </tr>
-  <td>spark.webui.yarn.useProxy</td>
+  <tr>
+    <td>spark.webui.yarn.useProxy</td>
     <td>false</td>
     <td>whether use yarn proxy url as spark weburl, e.g. http://localhost:8088/proxy/application_1583396598068_0004</td>
   </tr>
+  <tr>
+    <td>spark.repl.target</td>
+    <td>jvm-1.6</td>
+    <td>
+      Manually specifying the Java version of Spark Interpreter Scala REPL,Available options:<br/> 
+      scala-compile v2.10.7 to v2.11.12 supports "jvm-1.5, jvm-1.6, jvm-1.7 and jvm-1.8", and the default value is jvm-1.6.<br/> 
+      scala-compile v2.10.1 to v2.10.6 supports "jvm-1.5, jvm-1.6, jvm-1.7", and the default value is jvm-1.6.<br/> 
+      scala-compile v2.12.x defaults to jvm-1.8, and only supports jvm-1.8.
+    </td>
+  </tr>
 </table>
 
 Without any configuration, Spark interpreter works out of box in local mode. But if you want to connect to your Spark cluster, you'll need to follow below two simple steps.

spark/scala-2.10/src/main/scala/org/apache/zeppelin/spark/SparkScala210Interpreter.scala

@@ -67,10 +67,13 @@ class SparkScala210Interpreter(override val conf: SparkConf,
       sparkHttpServer = server
       conf.set("spark.repl.class.uri", uri)
     }
+    val target = conf.get("spark.repl.target", "jvm-1.6")
 
     val settings = new Settings()
     settings.embeddedDefaults(sparkInterpreterClassLoader)
     settings.usejavacp.value = true
+    settings.target.value = target
+
     this.userJars = getUserJars()
     LOGGER.info("UserJars: " + userJars.mkString(File.pathSeparator))
     settings.classpath.value = userJars.mkString(File.pathSeparator)

spark/scala-2.11/src/main/scala/org/apache/zeppelin/spark/SparkScala211Interpreter.scala

@@ -66,12 +66,14 @@ class SparkScala211Interpreter(override val conf: SparkConf,
       sparkHttpServer = server
       conf.set("spark.repl.class.uri", uri)
     }
+    val target = conf.get("spark.repl.target", "jvm-1.6")
 
     val settings = new Settings()
     settings.processArguments(List("-Yrepl-class-based",
       "-Yrepl-outdir", s"${outputDir.getAbsolutePath}"), true)
     settings.embeddedDefaults(sparkInterpreterClassLoader)
     settings.usejavacp.value = true
+    settings.target.value = target
 
     this.userJars = getUserJars()
     LOGGER.info("UserJars: " + userJars.mkString(File.pathSeparator))