[SPARK-15395][CORE] Use getHostString to create RpcAddress (backport …

…for 1.6)

## What changes were proposed in this pull request?

Backport apache#13185 to branch 1.6.

## How was this patch tested?

Jenkins unit tests.

Author: Shixiong Zhu <[email protected]>

Closes apache#13196 from zsxwing/host-string-1.6.

(cherry picked from commit 7ad82b6)

core/src/main/scala/org/apache/spark/rpc/netty/NettyRpcEnv.scala

@@ -585,7 +585,7 @@ private[netty] class NettyRpcHandler(
   private def internalReceive(client: TransportClient, message: ByteBuffer): RequestMessage = {
     val addr = client.getChannel().remoteAddress().asInstanceOf[InetSocketAddress]
     assert(addr != null)
-    val clientAddr = RpcAddress(addr.getHostName, addr.getPort)
+    val clientAddr = RpcAddress(addr.getHostString, addr.getPort)
     if (clients.putIfAbsent(client, JBoolean.TRUE) == null) {
       dispatcher.postToAll(RemoteProcessConnected(clientAddr))
     }
@@ -609,7 +609,7 @@ private[netty] class NettyRpcHandler(
   override def exceptionCaught(cause: Throwable, client: TransportClient): Unit = {
     val addr = client.getChannel.remoteAddress().asInstanceOf[InetSocketAddress]
     if (addr != null) {
-      val clientAddr = RpcAddress(addr.getHostName, addr.getPort)
+      val clientAddr = RpcAddress(addr.getHostString, addr.getPort)
       dispatcher.postToAll(RemoteProcessConnectionError(cause, clientAddr))
       // If the remove RpcEnv listens to some address, we should also fire a
       // RemoteProcessConnectionError for the remote RpcEnv listening address
@@ -629,7 +629,7 @@ private[netty] class NettyRpcHandler(
     val addr = client.getChannel.remoteAddress().asInstanceOf[InetSocketAddress]
     if (addr != null) {
       clients.remove(client)
-      val clientAddr = RpcAddress(addr.getHostName, addr.getPort)
+      val clientAddr = RpcAddress(addr.getHostString, addr.getPort)
       nettyEnv.removeOutbox(clientAddr)
       dispatcher.postToAll(RemoteProcessDisconnected(clientAddr))
       val remoteEnvAddress = remoteAddresses.remove(clientAddr)