StateTransferFileCacheLoaderFunctionalTest#testConcurrentStateTransfer can hang

The test can hang and will eventually be killed after the 5 minute timeout. The CI unfortunately doesn't count it as a failure. I have been seeing this quite often when running the core suite locally.

https://ci.infinispan.org/job/Infinispan/job/master/927

The stack in the log is:

Test org.infinispan.statetransfer.StateTransferFileCacheLoaderFunctionalTest.testConcurrentStateTransfer has been running for more than 300 seconds. Interrupting the test thread and dumping thread stacks of the test suite process and its children.
Dumping thread stacks of process 32404 to /home/infinispan/workspace/Infinispan_master-5OURPVBKVS5PLGVSKVWLBFUZPLIO2DZSV3U7HWSZJBYGBGKYSFXQ/core/threaddump-org_infinispan_statetransfer_StateTransferFileCacheLoaderFunctionalTest_testConcurrentStateTransfer-2018-11-02-32404.log
Interrupted thread testng-StateTransferFileCacheLoaderFunctionalTest (22).
Error dumping thread stacks/interrupting threads/killing processes:
[OK: 11616, KO: 1, SKIP: java.lang.InterruptedException
96] Test succeeded: org.infinispan.statetransfer.StateTransferFileCacheLoaderFunctionalTest.testConcurrentStateTransfer
at java.lang.Object.wait(Native Method)
at java.lang.Thread.join(Thread.java:1260)