borg_client: use absolute path to borg in borg_cmd

Using plain "borg" resolves to /usr/local/bin/borg which is the wrapper
for our main backup host. This causes the offsite backup to be executed
with BORG_REPO set to the main backup destination.

While the above doesn't cause any issues with the backup script/service,
because borg invocations specify the backup destination as an argument,
it's not ideal and/or correct. Adjust borg_cmd to include the full path
of /usr/bin/borg, thus removing any ambiguity.

roles/borg_client/defaults/main.yml

@@ -2,8 +2,8 @@ backup_hosts:
   - host: "ssh://u236610.your-storagebox.de:23"
     dir: "~/repo"
     suffix: ""
-    borg_cmd: "borg"
+    borg_cmd: "/usr/bin/borg"
   - host: "ssh://zh1905@zh1905.rsync.net:22"
     dir: "~/backup/{{ inventory_hostname }}"
     suffix: "-offsite"
-    borg_cmd: "borg --remote-path=borg1"
+    borg_cmd: "/usr/bin/borg --remote-path=borg1"

roles/borg_client/templates/borg.j2

 #!/bin/bash
 
-BORG_REPO="{{ item['host'] }}/{{ item['dir'] }}" exec /usr/bin/{{ item['borg_cmd'] }} "$@"
+BORG_REPO="{{ item['host'] }}/{{ item['dir'] }}" exec {{ item['borg_cmd'] }} "$@"