main: Set log handler for OSTree domain
main: Set log handler for OSTree domain

Now that OSTree is used as G_LOG_DOMAIN, set the main handler to match
so the appropriate messages are filtered. It would probably be more
appropriate to spell out "OSTree" in the code, but since G_LOG_DOMAIN is
being defined globally in the project, might as well reuse it here.

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

Closes: #225
Approved by: cgwalters

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