podman: make sure we remove the pulled image

Currently we pull test/image here but do not clean it out.  This
interferes with the buildset-registry podman tests that happen
afterwards when using podman 3.4.  It's unclear if this is a feature
or a bug, see [1].

[1] https://github.com/containers/podman/issues/13383

Change-Id: I722ba599fbc690d6cb967070c05215b98a73dcaf

playbooks/functional-test/podman.yaml

@@ -44,6 +44,9 @@
   register: image_list
   failed_when: "'test/image' not in image_list.stdout"
 
+- name: Remove the test image from the local cache, again
+  command: podman rmi localhost:9000/test/image
+
 - name: Try to pull an image that does not exist
   command: podman pull localhost:9000/test/dne
   register: result