Update certificate if the names change.

Create a new ACME challenge if the CSR changes (like when the list of
names change), thus creating a new certificate.

tasks/renew-cert.yaml

@@ -54,6 +54,7 @@
     acme_directory: *acme_directory
     acme_version: *acme_version
     csr: *csr_src
+    force: '{{ acme_csr is changed }}'
     fullchain_dest: &cert_src |-
         {{ playbook_dir }}/{{ host }}.crt
     modify_account: false