CI: Update cached cirros image to 0.5.3

Bifrost CI is currently failing to fetch the cirros image from cache:

    No such file or directory: '/opt/cache/files/cirros-0.5.1-x86_64-disk.img'

This may be caused by the removal of cirros-0.5.1 images from cache in
change Ibada405e0c1183559f428c749d0e54d0a45a2223.

Switch to cirros version 0.5.3 image instead.

Change-Id: I208182e65884d63548d78c68f676b899c562a2dc

playbooks/test-bifrost.yaml

@@ -18,7 +18,7 @@
     - block:
       - name: "Set variables if running in the CI"
         set_fact:
-           cirros_deploy_image_upstream_url: file:///opt/cache/files/cirros-0.5.1-x86_64-disk.img
+           cirros_deploy_image_upstream_url: file:///opt/cache/files/cirros-0.5.3-x86_64-disk.img
            copy_from_local_path: true
            git_url_root: "{{ lookup('env', 'WORKSPACE') }}"
       - name: "Check if openstacksdk is cloned"