Fix flaky test org.apache.cassandra.distributed.test.*RepairCoordinatorFastTest

[junit-timeout] Testcase: onlyCoordinator[SEQUENTIAL/true](org.apache.cassandra.distributed.test.FullRepairCoordinatorFastTest):	FAILED
[junit-timeout] nodetool command repair was successful but not expected to be. Actual: 0
[junit-timeout] junit.framework.AssertionFailedError: nodetool command repair was successful but not expected to be. Actual: 0
[junit-timeout] 	at org.apache.cassandra.distributed.api.NodeToolResult$Asserts.failure(NodeToolResult.java:76)
[junit-timeout] 	at org.apache.cassandra.distributed.test.RepairCoordinatorFast.onlyCoordinator(RepairCoordinatorFast.java:255)
[junit-timeout] 	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
[junit-timeout] 	at java.lang.Thread.run(Thread.java:748)