CI: use a dedicated disk for releases (#12692)

This should make 'no space left on device' problems easier to handle

Use /tmp/releases as local_release_dir CI created machine, while keeping
the same folder on the runner (needed for gitlab-ci runner pods)

tests/cloud_playbooks/roles/packet-ci/templates/vm.yml.j2

@@ -34,6 +34,10 @@ spec:
         - disk:
             bus: virtio
           name: cloudinitvolume
+        - disk:
+            bus: virtio
+          name: releases
+          serial: '2825A83CBDC8A32D5E'
       interfaces:
       - name: default
         bridge: {}
@@ -59,3 +63,6 @@ spec:
     - name: cloudinitvolume
       cloudInit{{ 'ConfigDrive' if cloud_image.startswith('flatcar') else 'NoCloud' }}:
         userDataBase64: '{{ ((ignition_config | to_json) if cloud_image.startswith('flatcar') else cloudinit_config) | b64encode }}'
+    - name: releases
+      emptyDisk:
+        capacity: '{{ releases_disk_size }}'