Move from broken ansible_fqdn variable to inventory_hostname

It seems to have broken with the release of filesystem 2021.12.07, which
incorporates this upstream change[1] in [2]. Please also see the
upstream issue[3].

I'm not sure why we used ansible_fqdn in the first place as
inventory_hostname should be preferred (as we define it ourselves).

[1] ce266330fc
[2] fc84245e3e
[3] https://github.com/systemd/systemd/issues/20358

roles/fail2ban/templates/jail.local.j2

@@ -13,7 +13,7 @@ usedns = no
 # if f2b ever needs to send emails, send them to root and make sure the sender
 # address clearly identifies the host the message originated from
 destemail = root
-sender = fail2ban@{{ansible_fqdn}}
+sender = fail2ban@{{inventory_hostname}}
 
 # use firewalld to manage bans - if we don't specify this, then fail2ban will
 # default to use iptables, which we don't want as our systems are running

roles/prometheus/templates/prometheus.yml.j2

@@ -31,7 +31,7 @@ scrape_configs:
     static_configs:
       - targets: ['127.0.0.1:9090']
         labels:
-          instance: "{{ ansible_fqdn }}"
+          instance: "{{ inventory_hostname }}"
 
   - job_name: prometheus-domain
     scheme: http
@@ -48,7 +48,7 @@ scrape_configs:
     static_configs:
       - targets: ['127.0.0.1:3100']
         labels:
-          instance: "{{ ansible_fqdn }}"
+          instance: "{{ inventory_hostname }}"
 
   - job_name: 'node_exporter'
     static_configs:

roles/promtail/templates/promtail.yaml.j2

@@ -28,7 +28,7 @@ scrape_configs:
         - localhost
         labels:
           job: nginx
-          instance: {{ ansible_fqdn }}
+          instance: {{ inventory_hostname }}
           __path__: /var/log/nginx/*/*.json
     pipeline_stages:
     - match:
@@ -46,7 +46,7 @@ scrape_configs:
         - localhost
         labels:
           job: pacman
-          instance: {{ ansible_fqdn }}
+          instance: {{ inventory_hostname }}
           __path__: /var/log/pacman.log
     pipeline_stages:
     - match: