[HOTFIX] Disable Spark UI in SparkSubmitSuite tests

This should fix a major cause of build breaks when running many parallel tests.

Author: JoshRosen

core/src/test/scala/org/apache/spark/deploy/SparkSubmitSuite.scala

@@ -260,6 +260,7 @@ class SparkSubmitSuite extends FunSuite with ShouldMatchers with ResetSystemProp
       "--class", SimpleApplicationTest.getClass.getName.stripSuffix("$"),
       "--name", "testApp",
       "--master", "local",
+      "--conf", "spark.ui.enabled=false",
       unusedJar.toString)
     runSparkSubmit(args)
   }
@@ -274,6 +275,7 @@ class SparkSubmitSuite extends FunSuite with ShouldMatchers with ResetSystemProp
       "--name", "testApp",
       "--master", "local-cluster[2,1,512]",
       "--jars", jarsString,
+      "--conf", "spark.ui.enabled=false",
       unusedJar.toString)
     runSparkSubmit(args)
   }