[SPARK-25887][K8S] Simplify logging statement

Author: rvesse

resource-managers/kubernetes/core/src/main/scala/org/apache/spark/deploy/k8s/SparkKubernetesClientFactory.scala

@@ -69,8 +69,7 @@ private[spark] object SparkKubernetesClientFactory extends Logging {
     // Allow for specifying a context used to auto-configure from the users K8S config file
     val kubeContext = sparkConf.get(KUBERNETES_CONTEXT).filter(_.nonEmpty)
     logInfo(s"Auto-configuring K8S client using " +
-      s"${if (kubeContext.isDefined) s"context ${kubeContext.getOrElse("?")}"
-      else "current context"}" +
+      kubeContext.map("context " + _).getOrElse("current context") +
       s" from users K8S config file")
 
     // Start from an auto-configured config with the desired context