test_backup_and_restore.py AssertionError fix
prefix in the backup function expects output to have
'ipa.ipaserver.install.ipa_backup.Backup:' and it's wrong. The right
one is 'ipaserver.install.ipa_backup:'.
https://pagure.io/freeipa/issue/7339
Reviewed-By: Felipe Volpone <fbarreto@redhat.com>