EZSPA-270 - adopt mapr spark feature to work in non-mapr env (apache#874)

- make "mapr.spark.user.secret" config optional
- review all mapr-specific volumes and make them optional

Author: AlexNavara

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

@@ -735,7 +735,7 @@ private[spark] object Config extends Logging {
     ConfigBuilder("spark.mapr.user.secret")
       .doc("Name of the mapr user secrets")
       .stringConf
-      .createWithDefault("mapr-user-secret")
+      .createOptional
 
   val KUBERNETES_AUTH_SUBMISSION_CONF_PREFIX =
     "spark.kubernetes.authenticate.submission"

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

@@ -130,15 +130,19 @@ private[spark] class MaprConfigFeatureStep(conf: KubernetesConf)
       .endVolumeMount()
   }
 
-  private def applyUserSecret(podBuilder: PodBuilder, containerBuilder: ContainerBuilder) = {
-    val userSecretName = sparkConf.get(MAPR_USER_SECRET).toString
+  private def applyUserSecret(podBuilder: PodBuilder, containerBuilder: ContainerBuilder): Unit = {
+    val userSecretName = sparkConf.get(MAPR_USER_SECRET)
     val userSecretVolumeName = s"$userSecretName-volume"
 
+    if (userSecretName.isEmpty) {
+      return
+    }
+
     podBuilder.editOrNewSpec()
       .addNewVolume()
         .withName(userSecretVolumeName)
         .withNewSecret()
-          .withSecretName(userSecretName)
+          .withSecretName(userSecretName.get)
         .endSecret()
       .endVolume()
       .endSpec()
@@ -167,6 +171,7 @@ private[spark] class MaprConfigFeatureStep(conf: KubernetesConf)
         .withName(serverSecretVolume)
         .withNewSecret()
           .withSecretName(serverSecretName)
+          .withOptional(true)
         .endSecret()
       .endVolume()
       .endSpec()
@@ -190,6 +195,7 @@ private[spark] class MaprConfigFeatureStep(conf: KubernetesConf)
       .addNewEnvFrom()
         .withNewConfigMapRef()
           .withName(clusterConfMap)
+          .withOptional(true)
         .endConfigMapRef()
       .endEnvFrom()
   }