Support TLS connection to Kafka

[ahamidi]

This PR adds support for TLS connections to Kafka. It introduces the following new properties to the Kafka configuration:

• TLSEnabled bool - Enable/Disable TLS
• CACertFile string - location of the CA certificate file
• ClientCertFile string - location of the client certificate file
• ClientCertKeyFile string - location of the client key file
• InsecureSkipVerify bool - Disable hostname verification (required if Kafka cluster uses self-signed certs).

Fixes #178

[mailgun-ci]

Can one of the admins verify this patch?

[horkhe]

@ahamidi so far so good :)

[ahamidi]

@horkhe I haven't had a chance to test it against a Kafka cluster yet, but hopefully will get a chance to in the next few days.

I noticed that not all configurations options were exposed directly as CLI flags. Was that a conscious decision to simplify the options? Should I trim the Kafka TLS options to the basics/most common?

[horkhe]

We only exposed bare minimum of command line parameters for simplest configuration option. Mostly to allow running kafka-pixy on a dev laptop for testing. In production kafka-pixy is supposed to run with only one cmd argument --config. Although I see no harm in exposing the TLS related command line arguments, if only to allow quick tests that TLS connections is working.

Please let me know how your testing goes. Also please squash all the commits with the commit message "Add support for TLS connection to Kafka".

And thanks again.

@thrawn01 do you have anything to add?

[thrawn01]

LGTM!

[ahamidi]

I was able to test this against Amazon MSK with TLS authentication enabled and it works as expected.

I'm not sure why the test is failing though (fails in multiplexer_test.go)