[SPARK-9649] Fix flaky test MasterSuite - randomize ports

```
Error Message

Failed to bind to: /127.0.0.1:7093: Service 'sparkMaster' failed after 16 retries!
Stacktrace

      java.net.BindException: Failed to bind to: /127.0.0.1:7093: Service 'sparkMaster' failed after 16 retries!
      at org.jboss.netty.bootstrap.ServerBootstrap.bind(ServerBootstrap.java:272)
      at akka.remote.transport.netty.NettyTransport$$anonfun$listen$1.apply(NettyTransport.scala:393)
      at akka.remote.transport.netty.NettyTransport$$anonfun$listen$1.apply(NettyTransport.scala:389)
      at scala.util.Success$$anonfun$map$1.apply(Try.scala:206)
      at scala.util.Try$.apply(Try.scala:161)
```

Author: Andrew Or <[email protected]>

Closes #7968 from andrewor14/fix-master-flaky-test and squashes the following commits:

fcc42ef [Andrew Or] Randomize port

Conflicts:
	core/src/test/scala/org/apache/spark/deploy/master/MasterSuite.scala

Author: Andrew Or

core/src/test/scala/org/apache/spark/deploy/master/MasterSuite.scala

@@ -81,6 +81,7 @@ class MasterSuite extends SparkFunSuite with Matchers with Eventually {
     conf.set("spark.deploy.recoveryMode", "CUSTOM")
     conf.set("spark.deploy.recoveryMode.factory",
       classOf[CustomRecoveryModeFactory].getCanonicalName)
+    conf.set("spark.master.rest.enabled", "false")
 
     val instantiationAttempts = CustomRecoveryModeFactory.instantiationAttempts
 
@@ -135,7 +136,7 @@ class MasterSuite extends SparkFunSuite with Matchers with Eventually {
     )
 
     val (actorSystem, port, uiPort, restPort) =
-      Master.startSystemAndActor("127.0.0.1", 7077, 8080, conf)
+      Master.startSystemAndActor("127.0.0.1", 0, 0, conf)
 
     try {
       Await.result(actorSystem.actorSelection("/user/Master").resolveOne(10 seconds), 10 seconds)

pom.xml

@@ -1256,6 +1256,7 @@
               <spark.test.home>${spark.test.home}</spark.test.home>
               <spark.testing>1</spark.testing>
               <spark.ui.enabled>false</spark.ui.enabled>
+              <spark.master.rest.enabled>false</spark.master.rest.enabled>
               <spark.ui.showConsoleProgress>false</spark.ui.showConsoleProgress>
               <spark.driver.allowMultipleContexts>true</spark.driver.allowMultipleContexts>
               <spark.unsafe.exceptionOnMemoryLeak>true</spark.unsafe.exceptionOnMemoryLeak>

project/SparkBuild.scala

@@ -514,6 +514,7 @@ object TestSettings {
     javaOptions in Test += "-Dspark.testing=1",
     javaOptions in Test += "-Dspark.port.maxRetries=100",
     javaOptions in Test += "-Dspark.ui.enabled=false",
+    javaOptions in Test += "-Dspark.master.rest.enabled=false",
     javaOptions in Test += "-Dspark.ui.showConsoleProgress=false",
     javaOptions in Test += "-Dspark.driver.allowMultipleContexts=true",
     javaOptions in Test += "-Dspark.unsafe.exceptionOnMemoryLeak=true",