This patch adds a new test, which verifies the TLS tracking.
Because we need to simulate SPF records, and Go does not support fully
intercepting DNS lookups yet, this test relies on dnsmasq to provide a
DNS resolver.
In the future, once Go supports DNS lookup interception, we can get rid
of this additional dependency.
This patch adds a Docker configuration file, to build an image that can
run the integration and stress tests.
It might be used for configuring automated testing infrastructure in
subsequent patches.