archusers: Allow overriding users' shell setting

Useful for mail.archlinux.org where this setting doesn't matter since we
force the SSH command to passwd and zsh was removed as part of the tools
cleanup effort recently (stops shadow.service from complaining about zsh
missing).

playbooks/mail.archlinux.org.yml

@@ -14,7 +14,7 @@
     - { role: rspamd, rspamd_dkim_domain: archlinux.org, tags: ["mail"] }
     - { role: unbound, unbound_port: 5353, tags: ["mail"] }
     - { role: postfwd, tags: ['mail'] }
-    - { role: archusers, archusers_ssh_options: 'command="/usr/bin/passwd",restrict,pty' }
+    - { role: archusers, shell_override: '/bin/bash', archusers_ssh_options: 'command="/usr/bin/passwd",restrict,pty' }
     - { role: fail2ban }
     - { role: prometheus_exporters }
     - { role: promtail }

roles/archusers/tasks/main.yml

@@ -15,7 +15,7 @@
     group: users
     groups: "{{ item.value.groups | join(',') }}"
     comment: "{{ item.value.name }}"
-    shell: "{{ item.value.shell | default('/bin/bash') }}"
+    shell: "{{ shell_override | default(item.value.shell | default('/bin/bash')) }}"
     password: ""
     update_password: on_create
     state: present