Enable hostname verification with verify option

[adamleko]

• fixes TLS certification validation not enforced #378

Checklist:

• Ensure PR doesn't contain untouched code reformatting: spaces, etc.
• Run flake8 and fix issues.
• Run pytest no tests failed. See https://clickhouse-driver.readthedocs.io/en/latest/development.html.

[adamleko]

I'd add unit tests for this but that depends on setting up a specific ClickHouse server to test against.

I think this change is straightforward enough as it is with a careful review, but if you have thoughts on how to set up your test environment and some pointers on how to access that I can take a crack at writing an integration test.

For manual testing you can verify that certificate validation failed by dumping out sock.getpeercert() after the socket.connect(sa) call in Connection._create_socket(…). This was always empty for me unless I set context.checkhostname to True - it seems as though that setting controls all certificate verification (both hostname verification and validating the certificate was signed by a trusted CA).

[coveralls]

Coverage: 84.901% (-11.6%) from 96.455% when pulling 5b25ab3 on adamleko:master into 18f28c6 on mymarilyn:master.