build: Set G_LOG_DOMAIN to OSTree
build: Set G_LOG_DOMAIN to OSTree

This will allow ostree programs to filter log messages specifically for
OSTree instead of using the NULL domain for ostree debugging.

https://bugzilla.gnome.org/show_bug.cgi?id=764237

Closes: #225
Approved by: cgwalters

gatispaeglis/ostree,gatispaeglis/ostree,gatispaeglis/ostree,gatispaeglis/ostree,GNOME/ostree,GNOME/ostree,gatispaeglis/ostree,GNOME/ostree,GNOME/ostree,gatispaeglis/ostree,GNOME/ostree