[TOREE-558] ScalaInterpreter prefer to use context classloader (#225)

Co-authored-by: Vincent Ye <vincent_ye@apple.com>
Co-authored-by: Cheng Pan <pan3793@gmail.com>

scala-interpreter/src/main/scala/org/apache/toree/kernel/interpreter/scala/ScalaInterpreter.scala

@@ -51,7 +51,9 @@ class ScalaInterpreter(private val config:Config = ConfigFactory.load) extends I
 
   protected val logger = LoggerFactory.getLogger(this.getClass.getName)
 
-  protected val _thisClassloader = this.getClass.getClassLoader
+  // honors caller's context classloader. If it isn't set, fall back to this class's classloader.
+  protected val _thisClassloader = Option(Thread.currentThread().getContextClassLoader)
+      .getOrElse(this.getClass.getClassLoader)
 
   protected val lastResultOut = new ByteArrayOutputStream()