This wires up the previously added OEM strings XML schema to be able to
generate comamnd line args for QEMU. This requires QEMU >= 2.12 release
containing this patch:

  commit 2d6dcbf93fb01b4a7f45a93d276d4d74b16392dd
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Sat Oct 28 21:51:36 2017 +0100

    smbios: support setting OEM strings table
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>