test(profiling): make sure we have sample before terminating process (#4175)

The current multiprocessing test wants to have at least one sample in the
generated pprof file. However, there's a tiny chance we don't have any event by
the time the profiler is stopped, which makes the test flaky.

Author: jd

tests/profiling/_test_multiprocessing.py

@@ -5,7 +5,16 @@
 
 
 def f():
-    time.sleep(1)
+    import ddtrace.profiling.bootstrap
+
+    profiler = ddtrace.profiling.bootstrap.profiler
+    for _ in range(50):
+        if any(map(len, profiler._recorder.events.values())):
+            break
+        time.sleep(0.1)
+    # Manually stop the profiler: atexit hooks are not called in subprocesses launched by multiprocessing and we want to
+    # be sure the profile are flushed out
+    profiler.stop()
 
 
 if __name__ == "__main__":