9621 Make createtxg and guid properties public

illumos/illumos-gate@e8d4a73c868afb740396041be80ed2b141065e76

Reviewed by: Andy Stormont <astormont@racktopsystems.com>
Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: Yuri Pankov <yuripv@yuripv.net>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Josh Paetzel <josh@tcbug.org>