ci: use OpenStack for spread tests

spread.yaml

@@ -15,21 +15,40 @@ include:
     - Makefile
     - rockcraft/
 
+#backends:
+#  google:
+#    key: '$(HOST: echo "$SPREAD_GOOGLE_KEY")'
+#    location: snapd-spread/us-east1-b
+#    halt-timeout: 2h
+#    systems:
+#      - ubuntu-20.04-64:
+#          workers: 1
+#          storage: 40G
+#      - ubuntu-22.04-64:
+#          workers: 4
+#          storage: 40G
+#      - fedora-39-64:
+#          workers: 1
+#          storage: 40G
+
 backends:
-  google:
-    key: '$(HOST: echo "$SPREAD_GOOGLE_KEY")'
-    location: snapd-spread/us-east1-b
+  openstack:
+    key: '$(HOST: echo "$SPREAD_OPENSTACK_ENV")'
+    plan: staging-cpu2-ram4-disk20
     halt-timeout: 2h
+    groups: [default]
     systems:
       - ubuntu-20.04-64:
+          image: ubuntu-focal-20.04-amd64
           workers: 1
           storage: 40G
       - ubuntu-22.04-64:
+          image: ubuntu-jammy-22.04-amd64
           workers: 4
           storage: 40G
-      - fedora-39-64:
-          workers: 1
-          storage: 40G
+#    - ubuntu-22.04-arm-64:
+#      image: ubuntu-jammy-22.04-arm64
+#      workers: 1
 
 prepare: |
   # if the 'tools' directory inside the submodule does not exist, then assume the submodule is empty