HUB and TAG variables ignored/not passed through to istioctl when running the tests

[peterj]

Prerequisites:

1. Run the prow/integ-suite-kind.sh --skip-build --skip-cleanup from the istio repo to set up the kind cluster
2. Set the following environment variables:

export DOCKER_HOST=unix:///var/run/docker.sock
export DOCKER_SOCKET_MOUNT="-v /var/run/docker.sock.raw:/var/run/docker.sock"
export TAG=latest
export HUB=gcr.io/istio-testing

3. Run the tests from the istio.io repo:

HUB=gcr.io/istio-testing TAG=latest TEST_ENV=kind ADDITIONAL_CONDITIONAL_HOST_MOUNTS="--mount type=bind,source=${HOME}/.ssh,destination=/home/user/.ssh,readonly " ADDITIONAL_CONTAINER_OPTIONS="--network host" make doc.test.profile-none TEST=ambient/getting-started/test.sh

The test hangs on the first step (installing ambient) because it fails to pull the istiod pilot image.

 k get deploy istiod -n istio-system -o yaml | grep image
        image: istio/pilot:1.23-alpha.6a089c8e9eaff7aa7e5bf8e1090a78fded2f7907-distroless
        imagePullPolicy: IfNotPresent

Even though we explicitly set the HUB and TAG variables, those are not being respected.

If I modify the snips.sh file and pass the --set tag=$TAG --set HUB=$HUB to the istioctl command, the test passes.