Ceph

From Josh:

I'm not sure if lttng is enabled in the release builds right now, but
we should change them to configure --without-lttng for now, for hammer.
There's a bad interaction with libvirt/apparmor/lttng [1] (and I'd
guess selinux too).

This only potentially affects trusty and fedora, since lttng is too old
(<2.4) in other releases.

We can keep it enabled on the gitbuilders so that it's still usable
without making users recompile ceph.

[1] https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1432644

Creating a ticket because the commits that add the flag are full of conflicts