Ensure we produce a valid JSON while emptying the file

It was detected this overrides breaks, at least, `podman network ls'
CLI.

Change-Id: I96382e655a03306f233963edb2aaa72953c7a531
Closes-Bug: #1889510
(cherry picked from commit dad6b77f0e)

tripleo_ansible/roles/tripleo_podman/tasks/tripleo_podman_install.yml

@@ -43,7 +43,7 @@
     - name: Remove default cni config for cni0 if exists
       copy:
         dest: /etc/cni/net.d/87-podman-bridge.conflist
-        content: ''
+        content: '{}'
         force: true
       when:
         - podman_bridge_config.stat.exists | bool