https://build.spring.io/browse/INT-MJATS41-1242
When different `DefaultLockRepository` instances use the same client id,
there is a possibility that they will update the same row in the table.
This way we have a chance that not only one obtains a lock and try to
add a value to the collection.
* Remove the test-case for the same client id as non-stable and even
dangerous by the the distributed lock purpose
* Use `tryLock(Long.MAX_VALUE)` to really ensure the wait behavior
during the concurrent loop
* Use `20` for thread pool to align with the tasks amount
**Cherry-picked to 4.3.x**
2fbb6fbaf4