Fix test in BlockFetcherIteratorSuite:

We now signal failures via Futures that throw exception, not Futures that
contain messages with hasError set.

Author: JoshRosen

core/src/main/scala/org/apache/spark/storage/BlockFetcherIterator.scala

@@ -137,7 +137,7 @@ object BlockFetcherIterator {
           }
         }
         case Failure(exception) => {
-          logError("Could not get block(s) from " + cmId)
+          logError("Could not get block(s) from " + cmId, exception)
           for ((blockId, size) <- req.blocks) {
             results.put(new FetchResult(blockId, -1, null))
           }

core/src/test/scala/org/apache/spark/storage/BlockFetcherIteratorSuite.scala

@@ -17,6 +17,7 @@
 
 package org.apache.spark.storage
 
+import java.io.IOException
 import java.nio.ByteBuffer
 
 import scala.collection.mutable.ArrayBuffer
@@ -146,9 +147,7 @@ class BlockFetcherIteratorSuite extends FunSuite with Matchers {
     when(blockManager.connectionManager).thenReturn(connManager)
 
     val f = future {
-      val message = Message.createBufferMessage(0)
-      message.hasError = true
-      message
+      throw new IOException("Send failed or we received an error ACK")
     }
     when(connManager.sendMessageReliably(any(),
       any())).thenReturn(f)