Add error handling during credentials onChange event so that the Scan Account feature does not activate if credentials are invalid

Because having to type the whole commands is a pain!

$ terratag -tags=var.default_tags
2020/09/24 23:09:46 Processing file cluster/ecs.tf
panic: invalid character 'v' looking for beginning of value

See the TODO in bin/codedeploy/AfterInstall.sh