run_switch.py: fix calls to exit()
diff --git a/run_switch.py b/run_switch.py
index 200c1aa..d5187b1 100755
--- a/run_switch.py
+++ b/run_switch.py
@@ -49,13 +49,13 @@
     check_call(["ls", ofd])
 except:
     print "Could not find datapath daemon: " + ofd
-    os.exit(1)
+    sys.exit(1)
 
 try:
     check_call(["ls", ofp])
 except:
     print "Could not find protocol daemon: " + ofp
-    os.exit(1)
+    sys.exit(1)
 
 if not options.no_wait:
     print "Starting ofprotocol in 2 seconds; ^C to quit"