Add a new secret usage type known as "tls" - it will handle adding the
secret objects for various TLS objects that need to provide some sort
of passphrase in order to access the credentials.
The format is:
<secret ephemeral='no' private='no'>
<description>Sample TLS secret</description>
<usage type='tls'>
<name>mumblyfratz</name>
</usage>
</secret>
Once defined and a passphrase set, future patches will allow the UUID
to be set in the qemu.conf file and thus used as a secret for various
TLS options such as a chardev serial TCP connection, a NBD client/server
connection, and migration.
Signed-off-by: John Ferlan <jferlan@redhat.com>
