X tests: Don't try to stop wcfs that is already exited

conftest.py

@@ -35,6 +35,9 @@ def pytest_unconfigure(config):
     print(wcfs._wcstarted)
     print("closing...")
     for wc in wcfs._wcstarted:
+        if wc._proc.poll() is not None:
+            continue # this wcfs server already exited
+
         twc = tWCFS(wc=wc)
         # FIXME currently has to kill wcfs.go, because swapned pinner threads are running
         #       -> stop pinner first