SPARK-2168 [Spark core] Use relative URIs for the app links in the History Server.

As agreed in PR #1160 adding test to verify if history server generates relative links to applications.

Author: Lukasz Jastrzebski <lukasz.jastrzebski@gmail.com>

Closes #4778 from elyast/master and squashes the following commits:

0c07fab [Lukasz Jastrzebski] Incorporating comments for SPARK-2168
6d7866d [Lukasz Jastrzebski] Adjusting test for  SPARK-2168 for master branch
d6f4fbe [Lukasz Jastrzebski] Added test for  SPARK-2168

core/src/test/scala/org/apache/spark/deploy/history/HistoryServerSuite.scala

+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.deploy.history
+
+import javax.servlet.http.HttpServletRequest
+
+import scala.collection.mutable
+
+import org.apache.hadoop.fs.Path
+import org.mockito.Mockito.{when}
+import org.scalatest.FunSuite
+import org.scalatest.Matchers
+import org.scalatest.mock.MockitoSugar
+
+import org.apache.spark.ui.SparkUI
+
+class HistoryServerSuite extends FunSuite with Matchers with MockitoSugar {
+
+  test("generate history page with relative links") {
+    val historyServer = mock[HistoryServer]
+    val request = mock[HttpServletRequest]
+    val ui = mock[SparkUI]
+    val link = "/history/app1"
+    val info = new ApplicationHistoryInfo("app1", "app1", 0, 2, 1, "xxx", true)
+    when(historyServer.getApplicationList()).thenReturn(Seq(info))
+    when(ui.basePath).thenReturn(link)
+    when(historyServer.getProviderConfig()).thenReturn(Map[String, String]())
+    val page = new HistoryPage(historyServer)
+
+    //when
+    val response = page.render(request)
+
+    //then
+    val links = response \\ "a"
+    val justHrefs = for {
+      l <- links
+      attrs <- l.attribute("href")
+    } yield (attrs.toString)
+    justHrefs should contain(link)
+  }
+}