Pass additional options to ./tools/test to revert to previous behaviour.

Previous commit upgrades Weave Net to the latest version of `build-tools`.
However, `./tools/test`'s default behaviour has changed, so we need to explicitly pass new options/arguments, in order to keep it behaving like before fd568682c3.

Makefile

@@ -210,7 +210,7 @@ $(SIGPROXY_EXE) $(TEST_TLS_EXE) $(WEAVEWAIT_NOOP_EXE) $(RUNNER_EXE):
 	go build $(BUILD_FLAGS) -o $@ ./$(@D)
 
 tests:
-	./tools/test -no-go-get
+	./tools/test -no-go-get -netgo -timeout 8m
 
 lint:
 	./tools/lint -nocomment -notestpackage .