'Delete a secret.
usage_type: one of \'iscsi\', \'ceph\', \'rbd\' or \'volume\'
usage_id: name of resource in secret'

def delete_secret(self, usage_type, usage_id):

    secret = self.find_secret(usage_type, usage_id)
    if (secret is not None):
        secret.undefine()
