[issue29136] Add OP_NO_TLSv1_3

[Christian Heimes]

Christian Heimes added the comment:

PR 1363 also introduced ssl.HAS_TLSv1_3 flag for unit tests. The flag is required because OpenSSL 1.1.1-dev can be compiled without TLS 1.3 support. The development version always defines OP_NO_TLSv1_3 to a non-zero value. Further more the PR adds a test for TLS 1.3.

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versions:  -Python 3.5

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