https://build.spring.io/browse/INT-MASTER-901
The `JdbcLockRegistryDifferentClientTests.testOnlyOneLock()` relies
on the `ArrayList.isEmpty()` state to proceed with the logic.
But since the `ArrayList.size` property is not `volatile`, there is no
guarantee for the proper state in the multi-threaded environment like
we have in this test-case.
* Replace `ArrayList` in the test with the `LinkedBlockingQueue` which
already rely on the `AtomicInteger` for the `size` property
* Fix `JdbcLockRegistry` tests to shutdown used `ExecutorService` s
to ensure set free threads after test suite execution.
**Cherry-pick to 4.3.x**
2736de99de