test: do not close/recreate the asyncio event loop (WA for asyncio bugs when multiple tests are run)

artiq/test/pc_rpc.py

@@ -74,10 +74,7 @@ class RPCCase(unittest.TestCase):
 
     def _loop_asyncio_echo(self):
         loop = asyncio.get_event_loop()
-        try:
         loop.run_until_complete(self._asyncio_echo())
-        finally:
-            loop.close()
 
     def test_asyncio_echo(self):
         self._run_server_and_test(self._loop_asyncio_echo)

artiq/test/worker.py

@@ -41,12 +41,8 @@ def _run_experiment(experiment):
     }
 
     worker = Worker(handlers)
-    loop = asyncio.new_event_loop()
-    asyncio.set_event_loop(loop)
-    try:
+    loop = asyncio.get_event_loop()
     loop.run_until_complete(_call_worker(worker, run_params))
-    finally:
-        loop.close()
 
 
 class WatchdogCase(unittest.TestCase):