new treenames: gnome-ostree/buildmaster/x86_64-{runtime,devel}

[Colin Walters <walters verbum org>]

See:
http://git.gnome.org/browse/gnome-ostree/commit/?id=d8a0f018ad7a083a403fc24f766b2eca75be77ea

The upshot of this is that you will need to change your deployment from
whatever you were using before (e.g. trees/gnomeos-3.8-x86_64-runtime),
to one of the new trees (e.g. gnome-ostree/buildmaster/x86_64-runtime).

I recommend just rerunning the install command:

$ ostree admin install http://ostree.gnome.org/gnome-ostree.cfg

The minor downside of this is that the old treenames stay in the repo
config and will be fetched; but you can safely delete them by
editing /ostree/repo/config manually.