Fix vehicle tests

vehicle/config_test.go

@@ -18,8 +18,8 @@ func TestVehicles(t *testing.T) {
 		"Missing required parameter", // Renault
 		"error connecting: Network Error",
 		"unexpected status: 401",
-		"could not obtain token",        // Porsche
-		"login failed: 400 Bad Request", // Tesla
+		"could not obtain token", // Porsche
+		"missing credentials",    // Tesla
 	}
 
 	for _, tmpl := range test.ConfigTemplates("vehicle") {

vehicle/tesla.go

@@ -50,6 +50,10 @@ func NewTeslaFromConfig(other map[string]interface{}) (api.Vehicle, error) {
 		return nil, err
 	}
 
+	if cc.User == "" && cc.Tokens.Access == "" {
+		return nil, errors.New("missing credentials")
+	}
+
 	v := &Tesla{
 		embed: &embed{cc.Title, cc.Capacity},
 	}