smbserver: pin Python version to 2 since we are not yet 3 compatible

Even though the existing code can be fixed to run on Python 3, the
tests will fail due to the Unicode transition the protocol is invalid.

Follow up to ee63837
Closes #5085

tests/smbserver.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2
 # -*- coding: utf-8 -*-
 #
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