Merge branch 'add_target_prometheus_exporters' into 'master'

Add correct After targets for prometheus_exporters

See merge request !297

roles/prometheus_exporters/templates/prometheus-arch-textcollector.service.j2

 [Unit]
 Description=Prometheus Arch Exporter
-After=network.target
+Wants=network-online.target
+After=network-online.target
 
 [Service]
 Type=oneshot

roles/prometheus_exporters/templates/prometheus-btrfs-textcollector.service.j2

 [Unit]
 Description=Prometheus btrfs Exporter
+Wants=network-online.target
+After=network-online.target
 
 [Service]
 Type=oneshot

roles/prometheus_exporters/templates/prometheus-rebuilderd-textcollector.service.j2

 [Unit]
 Description=Prometheus Rebuilderd Exporter
-After=network.target
+After=rebuilderd.service
 
 [Service]
 Type=oneshot