Improve `curl` command for testing the application (#2945)
Improve `curl` command for testing the application (#2945)

When I tried testing the application with `curl`, I got `000` as response.
For my environment, escaping the braces results in the variable not being expanded.
But because of outputting to `/dev/null`, I didn't see the error message `curl: (6) Could not resolve host: ${GATEWAY_URL}`

I'm using zsh under macOS.
geeknoid/istio.github.io,geeknoid/istio.github.io,istio/istio.io,istio/istio.io,geeknoid/istio.github.io,istio/istio.io,geeknoid/istio.github.io,geeknoid/istio.github.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io