TestAuthValidator is not cleaning up created cluster causing TestClusterAccessor to fail

[xyuanlu]

Describe the bug

2022-05-15T20:32:53.2585338Z [ERROR] Tests run: 205, Failures: 1, Errors: 0, Skipped: 35, Time elapsed: 146.079 s <<< FAILURE! - in TestSuite
2022-05-15T20:32:53.2585806Z [ERROR] testGetClusters(org.apache.helix.rest.server.TestClusterAccessor)  Time elapsed: 0.219 s  <<< FAILURE!
2022-05-15T20:32:53.2587133Z java.lang.AssertionError: clusters from response: [TestCluster_0, TaskTestCluster, TestCluster_1, superCluster, TestCluster_2, TestCluster_3, StoppableTestCluster, testDefaultAuthValidator, testCustomAuthValidator] vs clusters actually: [TestCluster_0, TaskTestCluster, TestCluster_1, superCluster, TestCluster_2, TestCluster_3, StoppableTestCluster]: lists don't have the same size expected:<7> but was:<9>
2022-05-15T20:32:53.2588018Z 	at org.apache.helix.rest.server.TestClusterAccessor.testGetClusters(TestClusterAccessor.java:102)

To Reproduce

CI test failure.

Should add an afterClass to clean up.