python 2.7 test_ssl hits AttributeError with openssl 1.1.1

[Dimitri John Ledkov]

autopkgtest fails with openssl1.1.1

As seen at:
https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-cosmic/cosmic/amd64/p/python2.7/20180927_033108_115d8@/log.gz

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ERROR: test_tls1_3 (test.test_ssl.ThreadedTests)
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Traceback (most recent call last):
  File "/usr/lib/python2.7/test/test_ssl.py", line 2815, in test_tls1_3
    with context.wrap_socket(socket.socket()) as s:
AttributeError: __exit__