Revert "[SPARK-21642][CORE] Use FQDN for DRIVER_HOST_ADDRESS instead of ip address" (apache-spark-on-k8s#255)

This reverts commit d695a52.

Author: ash211

core/src/main/scala/org/apache/spark/internal/config/package.scala

@@ -253,7 +253,7 @@ package object config {
   private[spark] val DRIVER_HOST_ADDRESS = ConfigBuilder("spark.driver.host")
     .doc("Address of driver endpoints.")
     .stringConf
-    .createWithDefault(Utils.localCanonicalHostName())
+    .createWithDefault(Utils.localHostName())
 
   private[spark] val DRIVER_BIND_ADDRESS = ConfigBuilder("spark.driver.bindAddress")
     .doc("Address where to bind network listen sockets on the driver.")

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -936,13 +936,6 @@ private[spark] object Utils extends Logging {
     customHostname = Some(hostname)
   }
 
-  /**
-   * Get the local machine's FQDN.
-   */
-  def localCanonicalHostName(): String = {
-    customHostname.getOrElse(localIpAddress.getCanonicalHostName)
-  }
-
   /**
    * Get the local machine's hostname.
    */