YARN-8974. Improve the assertion message in TestGPUResourceHandler. (Zhankun Tang via wangda)

Change-Id: I4eb58e9d251d5f54e7feffc4fbb813b4f5ae4b1b

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/test/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/linux/resources/gpu/TestGpuResourceHandler.java

@@ -465,7 +465,7 @@ public class TestGpuResourceHandler {
       caughtException = true;
     }
     Assert.assertTrue(
-        "Should fail since requested device Id is not in allowed list",
+        "Should fail since requested device Id is already assigned",
         caughtException);
 
     // Make sure internal state not changed.