Merge pull request #535 from nemith/master

Add deprecation warning to go.mod

Test a mock connection over real TLS

Refactors the TLS test to satisfy a complete TLS+AMQP handshake instead
of only checking for the initial frame.

This will either timeout on server accepting a connection (no TLS) or
the test failing (end to end).

Lints the startTlsServer for go1.11