Add buffer result for generating vendor configs

Add buffers to verify the success of generating and restoring vendor
configs.

Bug: 281835821
Test: atest android.car.apitest.CarPropertyManagerTest
Change-Id: Ic3cb8bf3e606847ff55d719900ad0b764b56aaf4
diff --git a/automotive/vehicle/aidl/impl/fake_impl/hardware/src/FakeVehicleHardware.cpp b/automotive/vehicle/aidl/impl/fake_impl/hardware/src/FakeVehicleHardware.cpp
index 4934771..0f8da00 100644
--- a/automotive/vehicle/aidl/impl/fake_impl/hardware/src/FakeVehicleHardware.cpp
+++ b/automotive/vehicle/aidl/impl/fake_impl/hardware/src/FakeVehicleHardware.cpp
@@ -1015,9 +1015,11 @@
     } else if (EqualsIgnoreCase(option, "--genTestVendorConfigs")) {
         mAddExtraTestVendorConfigs = true;
         result.refreshPropertyConfigs = true;
+        result.buffer = "successfully generated vendor configs";
     } else if (EqualsIgnoreCase(option, "--restoreVendorConfigs")) {
         mAddExtraTestVendorConfigs = false;
         result.refreshPropertyConfigs = true;
+        result.buffer = "successfully restored vendor configs";
     } else {
         result.buffer = StringPrintf("Invalid option: %s\n", option.c_str());
     }