Fix incorrect xauth check in AbstractDisplay

The check incorrectly checked against the xauth module, instead of
checking against use_xauth.

Author: sebastian-correa

sbvirtualdisplay/abstractdisplay.py

@@ -22,7 +22,7 @@ def __init__(self, use_xauth=False):
             USED_DISPLAY_NR_LIST.append(self.display)
         finally:
             mutex.release()
-        if xauth and not xauth.is_installed():
+        if use_xauth and not xauth.is_installed():
             raise xauth.NotFoundError()
         self.use_xauth = use_xauth
         self._old_xauth = None