[SPARK-11314][BUILD][HOTFIX] Add exclusion for moved YARN classes.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #10147 from vanzin/SPARK-11314.

project/MimaExcludes.scala

@@ -159,7 +159,10 @@ object MimaExcludes {
         // SPARK-3580 Add getNumPartitions method to JavaRDD
         ProblemFilters.exclude[MissingMethodProblem](
           "org.apache.spark.api.java.JavaRDDLike.getNumPartitions")
-      )
+      ) ++
+      // SPARK-11314: YARN backend moved to yarn sub-module and MiMA complains even though it's a
+      // private class.
+      MimaBuild.excludeSparkClass("scheduler.cluster.YarnSchedulerBackend$YarnSchedulerEndpoint")
     case v if v.startsWith("1.5") =>
       Seq(
         MimaBuild.excludeSparkPackage("network"),