[BUG] CacheData::cleanUpOnExit kills QThread objects too quickly

[lohedges]

After cleaning a PageCache via CacheData::cleanUpOnExit, threads are killed if they don't stop within a 50ms wait. On my Linux box, this causes intermittent crashes on interpreter exit since threads are killed because the did not stop within the wait period. Increasing this to 100ms seems to fix the issue for me. Perhaps it's also possible to terminate the thread and catch the exception thrown?