template brain_backup - add condition for backup_id

templates/brain_backup.j2

@@ -84,7 +84,9 @@ find $backup_dir -type d -ctime +$backup_local_retention -exec rm -rf {} \;
 
 ## send to PBS ##
 /usr/bin/proxmox-backup-client backup slash.pxar:/ \
---backup-id {{ backup_host_id | default({{ ansible_hostname }}) }} \
+{% if backup_host_id is defined %}
+--backup-id {{ backup_host_id }} \
+{% endif %}
 {% if backup_path_include is defined %}
 {% for item in backup_path_include %}
 {% if item.fs_mount is defined %}--include-dev {{ item.path }} \{% endif %}