[session] move context manager logic in the security context manager The `init_security` and `reset_security` method have no other user that the context manager itself. Having dedicated public function is not useful.

from os.path import join
assert __file__.endswith(join('scripts', 'script2.py')), __file__
assert '__main__' == __name__, __name__
assert ['-v'] == __args__, __args__