test: Add TLS tracking integration test

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.

test/util/lib.sh

@@ -11,7 +11,7 @@ function init() {
 	cd ${TBASE}
 
 	if [ "${RACE}" == "1" ]; then
-		RACE="-race"
+		GOFLAGS="$GOFLAGS -race"
 	fi
 
 	# Remove the directory where test-mda will deliver mail, so previous
@@ -30,7 +30,7 @@ function chasquid() {
 		return
 	fi
 
-	( cd ${TBASE}/../../; go build ${RACE} . )
+	( cd ${TBASE}/../../; go build $GOFLAGS -tags="$GOTAGS" . )
 
 	# HOSTALIASES: so we "fake" hostnames.
 	# PATH: so chasquid can call test-mda without path issues.
@@ -45,7 +45,8 @@ function chasquid_cover() {
 	# Build the coverage-enabled binary.
 	# See coverage_test.go for more details.
 	( cd ${TBASE}/../../;
-	  go test -covermode=count -coverpkg=./... -c -tags coveragebin )
+	  go test -covermode=count -coverpkg=./... -c \
+		  -tags="coveragebin $GOTAGS" $GOFLAGS )
 
 	# Run the coverage-enabled binary, named "chasquid.test" for hacky
 	# reasons.  See the chasquid function above for details on the