Borg ignore ansible tmp files

If borg sees an ansible tmp file just before it is removed by ansible
then we can get errors of this form when running borg:

  stat: [Errno 2] No such file or directory: '/root/.ansible/tmp/ansible-tmp-$IDENTIFIER'

This causes the backup run to report failure. Address this by adding
/root/.ansible/tmp/* to our borg backup excludes list.

Change-Id: Ie2c7081a4510959f6514b1cb7eb8facc4ac129fb

playbooks/roles/borg-backup/defaults/main.yaml

@@ -3,6 +3,7 @@ borg_backup_excludes:
   - '/etc/project-config/*'
   - '/home/*.cache/*'
   - '/root/*.cache/*'
+  - '/root/.ansible/tmp/*'
   - '/root/.bup*'
   - '/var/cache/*'
   - '/var/tmp/*'