Low Zaza test coverage

[Aurelien Lourot]

We have Zaza tests for the barbican charm [0] in which we test creating and deleting secrets, but with no real backend (neither barbican-vault nor SoftHSM).

The Zaza tests for the barbican-vault charm [1] only validate unsealing the vault.

We need Zaza tests validating the creation and deletion of secrets when barbican-vault is involved.

0: https://github.com/openstack-charmers/zaza-openstack-tests/blob/master/zaza/openstack/charm_tests/barbican/tests.py#L58
1: https://github.com/openstack-charmers/zaza-openstack-tests/blob/master/zaza/openstack/charm_tests/barbican_vault/tests.py