packer/windows/conf/bin/bk-install-elastic-stack.sh: Do clobber some variables.

These variables are more like a statement of fact about the stack you're running on, than settings
you can meaningfully tweak.  So, we still choose to override them.

Author: toothbrush

packer/windows/conf/bin/bk-install-elastic-stack.ps1

@@ -71,15 +71,15 @@ function set_always() {
 
 Add-Content -Path C:\buildkite-agent\cfn-env -Value @"
 
+set_always         "BUILDKITE_AGENTS_PER_INSTANCE" "$Env:BUILDKITE_AGENTS_PER_INSTANCE"
+set_always         "BUILDKITE_ECR_POLICY" "$Env:BUILDKITE_ECR_POLICY"
+set_always         "BUILDKITE_SECRETS_BUCKET" "$Env:BUILDKITE_SECRETS_BUCKET"
+set_always         "BUILDKITE_STACK_NAME" "$Env:BUILDKITE_STACK_NAME"
+set_always         "BUILDKITE_STACK_VERSION" "$Env:BUILDKITE_STACK_VERSION"
+set_always         "DOCKER_VERSION" "$DOCKER_VERSION"
+set_always         "PLUGINS_ENABLED" "$PLUGINS_ENABLED"
 set_unless_present "AWS_DEFAULT_REGION" "$Env:AWS_REGION"
 set_unless_present "AWS_REGION" "$Env:AWS_REGION"
-set_unless_present "BUILDKITE_AGENTS_PER_INSTANCE" "$Env:BUILDKITE_AGENTS_PER_INSTANCE"
-set_unless_present "BUILDKITE_ECR_POLICY" "$Env:BUILDKITE_ECR_POLICY"
-set_unless_present "BUILDKITE_SECRETS_BUCKET" "$Env:BUILDKITE_SECRETS_BUCKET"
-set_unless_present "BUILDKITE_STACK_NAME" "$Env:BUILDKITE_STACK_NAME"
-set_unless_present "BUILDKITE_STACK_VERSION" "$Env:BUILDKITE_STACK_VERSION"
-set_unless_present "DOCKER_VERSION" "$DOCKER_VERSION"
-set_unless_present "PLUGINS_ENABLED" "$PLUGINS_ENABLED"
 "@
 
 If ($Env:BUILDKITE_AGENT_RELEASE -eq "edge") {