Add workflow to define runner name

Author: MaxBed4d

.github/workflows/runs-on-preq.yml

@@ -0,0 +1,26 @@
+---
+name: Create output for `runs-on` variable
+
+on:
+  workflow_call:
+    inputs:
+      runner_env:
+        description: 'The environment input from caller workflow'
+        default: 'SMS Lab'
+        required: True
+        type: string
+    outputs:
+      runner_name_image_build:
+        description: "Image builder runner name"
+        value: ${{ jobs.define_runner.outputs.image-build-runner }}
+      runner_name_aio:
+        description: "AiO runner name"
+        value: ${{ jobs.define_runner.outputs.aio-runner }}
+
+jobs:
+  define_runner:
+    environment: ${{ inputs.runner_env }}
+    runs-on: ubuntu-latest
+    outputs:
+      image-build-runner: ${{ vars.RUNS_ON_TARGET_IMAGE_BUILDER }}
+      aio-runner: ${{ vars.RUNS_ON_TARGET_AIO }}

.github/workflows/stackhpc-container-image-build.yml

@@ -113,11 +113,22 @@ jobs:
         run : |
           echo "Environment variable RUNS_ON_TARGET_IMAGE_BUILDER: ${{ vars.RUNS_ON_TARGET_IMAGE_BUILDER }}"
 
+  runner-preqs:
+    name: Generate runs-on target based on environment 
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+       # This is because there is a bug where the runs-on target cannot be dynamically set using environment variables. 
+      - name: Call setup workflow
+        uses: ./.github/workflows/runs-on-preq.yml
+
+
   container-image-build:
     name: Build Kolla container images
     if: github.repository == 'stackhpc/stackhpc-kayobe-config'
     environment: ${{ inputs.runner_env }}
-    runs-on: ${{ vars.RUNS_ON_TARGET_IMAGE_BUILDER }}
+    runs-on: ${{ needs.runner-preqs.outputs.runner_name_image_build }}
     timeout-minutes: 720
     permissions: {}
     strategy: