Extend ROS2 support Step 0: Stabilize server unit tests

streaming.stream_outlives_server was often segfaulting.
This fixes the issue. At least the test runs with 100 repetition
without any issue. Previously one was lucky if 10 repetitions succeed.

Author: berndgassmann

LibCarla/source/carla/ThreadPool.h

@@ -16,6 +16,7 @@
 
 #include <future>
 #include <thread>
+#include <chrono>
 #include <type_traits>
 
 namespace carla {
@@ -29,6 +30,11 @@ namespace carla {
     /// Stops the ThreadPool and joins all its threads.
     ~ThreadPool() {
       Stop();
+      // Give some time to boost asio to properly stop.
+      // below 20ms this might be useless if there is heavy load.
+      // Without this, segmentation faults were observed
+      // within the boost asio code on destruction of the io_context.
+      std::this_thread::sleep_for(std::chrono::milliseconds(20));
     }
 
     /// Return the underlying io_context.