Ignore OSError when checking for config file changes.

gns3server/config.py

@@ -110,8 +110,11 @@ class Config(object):
 
         changed = False
         for file in self._watched_files:
+            try:
                 if os.stat(file).st_mtime != self._watched_files[file]:
                     changed = True
+            except OSError:
+                continue
         if changed:
             self.read_config()
         for section in self._override_config: