test/ctlmgr: keep trying to ping on OSError

Since Python 3.5.2, this exception can be raised on Windows when the
connection fails.

artiq/test/test_ctlmgr.py

@@ -50,7 +50,8 @@ class ControllerCase(unittest.TestCase):
             except asyncio.TimeoutError:
                 timeout -= dt
             except (ConnectionAbortedError, ConnectionError,
-                    ConnectionRefusedError, ConnectionResetError):
+                    ConnectionRefusedError, ConnectionResetError,
+                    OSError):
                 await asyncio.sleep(dt)
                 timeout -= dt
         raise asyncio.TimeoutError