b/144429078: replace nginx with endpoint in serverless image build script
b/144429078: replace nginx with endpoint in serverless image build script

Change-Id: I634ea0f997d2edadc21d80ecaef869a36f08cf6b

GoogleCloudPlatform/esp-v2,GoogleCloudPlatform/esp-v2,GoogleCloudPlatform/esp-v2,GoogleCloudPlatform/esp-v2,GoogleCloudPlatform/esp-v2