test_integration: backup custodia conf and keys
    
    Add an integration test for issue 7247 (ipa-backup does not backup
    Custodia keys and files)
    The test performs backup / uninstall / check custodia files were removed /
    restore and check that the custodia conf and keys files are restored.
    
    related ticket https://pagure.io/freeipa/issue/7247
    
    Reviewed-By: Christian Heimes <cheimes@redhat.com>