[atomic-devel] Direct LVM by default

[Colin Walters <walters verbum org>]

Per previous discussion, I've been working on redoing the default Atomic
setup to use direct LVM.  This is faster than loopback, and improves
management ability.

See:
https://bugzilla.redhat.com/show_bug.cgi?id=1145660
https://github.com/projectatomic/rpm-ostree-toolbox/commit/0c7b373f6037d1f1d2ad2a46db0484721def44a8

Since we're still using -toolbox for CentOS, we should be able to
upgrade there and spin a new cloud image from that.  For Fedora, I still
need to land patches to the new compose tooling for this that uses
Anaconda.

Some open items:

* How much space for the OS?  I chose 3G, given the host is 1G, leaving
plenty for upgrades and host data.  But should we try for less?  More?
* How big should the disk be in general?  I chose 16G, reasoning that
right now Docker containers are limited to 10G by default, so you can at
least have a full one, plus other small ones.

Of course, thanks to LVM all of this is mutable after the fact - you can
attach other storage and migrate there.