Now that the trivial keymaster supports multiple keys, let's not
forget about the KMS/Barbican keymaster. Additional keys are
configured as:
key_id_<secret_id> = <KMS unique identifier>
As with the trivial keymaster, the key to use for PUTs and POSTs is
specified with:
active_root_secret_id = <secret_id>
Change-Id: I4f485dcb31e5bea511c4e539c54681091fc5bb1c