test: Remove dependency on wget

This patch removes the dependency on wget for fetching content over
http, which was used in one of the tests to do some checking on debug
and metric pages, as well as loop detection.

Instead of wget, we now use a small built-in utility called fexp.

test/util/lib.sh

@@ -118,6 +118,11 @@ function minidns_bg() {
 	MINIDNS=$!
 }
 
+function fexp() {
+	( cd ${UTILDIR}; go build fexp.go )
+	${UTILDIR}/fexp "$@"
+}
+
 function success() {
 	echo success
 }