bigtable.mirroring.core.bufferedmutator.TestConcurrentMirroringBufferedMutator: testErrorsReportedBySecondaryAreReportedAsWriteErrors failed

Note: #3879 was also for this test, but it was closed more than 10 days ago. So, I didn't mark it flaky.

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commit: 489b463d42032efb86c9b2b56fa6c7c091ecd563
buildURL: [Build Status](https://source.cloud.google.com/results/invocations/1a1d96a0-1738-4d47-88f5-fae77f645cd9), [Sponge](http://sponge2/1a1d96a0-1738-4d47-88f5-fae77f645cd9)
status: failed
Test output

org.apache.hadoop.hbase.client.RetriesExhaustedWithDetailsException: Failed 2 actions: IOException: 2 times, servers with issues: invalid.example:1234

	at com.google.cloud.bigtable.mirroring.core.bufferedmutator.ConcurrentMirroringBufferedMutator$RetriesExhaustedExceptionBuilder.clearAndBuild(ConcurrentMirroringBufferedMutator.java:349)

	at com.google.cloud.bigtable.mirroring.core.bufferedmutator.ConcurrentMirroringBufferedMutator.throwExceptionIfAvailable(ConcurrentMirroringBufferedMutator.java:306)

	at com.google.cloud.bigtable.mirroring.core.bufferedmutator.ConcurrentMirroringBufferedMutator.mutateScoped(ConcurrentMirroringBufferedMutator.java:108)

	at com.google.cloud.bigtable.mirroring.core.bufferedmutator.MirroringBufferedMutator.mutate(MirroringBufferedMutator.java:203)

	at com.google.cloud.bigtable.mirroring.core.bufferedmutator.TestConcurrentMirroringBufferedMutator.testErrorsReportedBySecondaryAreReportedAsWriteErrors(TestConcurrentMirroringBufferedMutator.java:316)

	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

	at java.lang.reflect.Method.invoke(Method.java:498)

	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)

	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)

	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)

	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)

	at org.mockito.internal.junit.JUnitSessionStore$1.evaluateSafely(JUnitSessionStore.java:55)

	at org.mockito.internal.junit.JUnitSessionStore$1.evaluate(JUnitSessionStore.java:43)

	at org.junit.rules.ExternalResource$1.evaluate(ExternalResource.java:54)

	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)

	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)

	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)

	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)

	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)

	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)

	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)

	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)

	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)

	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)

	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)

	at org.junit.runners.ParentRunner.run(ParentRunner.java:413)

	at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:365)

	at org.apache.maven.surefire.junit4.JUnit4Provider.executeWithRerun(JUnit4Provider.java:273)

	at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:238)

	at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:159)

	at org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:384)

	at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:345)

	at org.apache.maven.surefire.booter.ForkedBooter.execute(ForkedBooter.java:126)

	at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:418)