The test/t-14-tls_tracking test relies on Go 1.8 features, but since we
used to support Go 1.7, the test had a version check.
Since now the minimum Go version supported is 1.9, we can remove this
check.
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.
