This change adds support to the Barbican key manager for configuring a
service user. This can be used to provide additional security through
the combination of a user token and a service token, with appropriate
modifications to Barbican API policy.
Use of a service user is enabled via the [barbican]
send_service_user_token option, which defaults to False. When set to
True, the service user is configured via keystoneauth options in the
barbican_service_user group.
Change-Id: I143cb57c8534a8dc0a91e6e42917dd0c134170c0
162039467a