feat(ooniprobe): add vanilla_tor to experimental (#745)

While there make vanilla_tor only run in unattended mode.

While there also make torsf unattended-mode only.

See https://github.com/ooni/probe/issues/2101

See https://github.com/ooni/probe/issues/2057

cmd/ooniprobe/internal/nettests/vanillator.go

@@ -0,0 +1,16 @@
+package nettests
+
+// VanillaTor test implementation
+type VanillaTor struct {
+}
+
+// Run starts the test
+func (h VanillaTor) Run(ctl *Controller) error {
+	builder, err := ctl.Session.NewExperimentBuilder("vanilla_tor")
+	if err != nil {
+		return err
+	}
+	return ctl.Run(builder, []string{""})
+}
+
+func (h VanillaTor) onlyBackground() {}