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 <firstname.lastname@example.org>