Prevent overriding faulthandler settings (#3668)

This change ensures that Ray set up fault handlers only if it has not been enabled by other applications. Otherwise some applications could face strange issues when using Ray, and some unittests using xml runners will fail.

python/ray/worker.py

@@ -1830,7 +1830,8 @@ def connect(ray_params,
     assert worker.cached_functions_to_run is not None, error_message
 
     # Enable nice stack traces on SIGSEGV etc.
-    faulthandler.enable(all_threads=False)
+    if not faulthandler.is_enabled():
+        faulthandler.enable(all_threads=False)
 
     if ray_params.collect_profiling_data:
         worker.profiler = profiling.Profiler(worker)