Propagate trace format all the way to the consumer

Propagate trace format all the way to the consumer

TODO: currently we end up propagating and exposing the trace format as a
vulgar integer on lttng-consumerd side. This is one of the frontier we
discussed IRL.

TODO: use the trace format serialize and pass a complete trace format
object on the pipe

Note that this is necessary to later decide if the consumerd strips the
ringbuffer header or not based on the ctf version. As discussed IRL, ust
could be modified to expose an API allowing us to set the ctf version thus
propagating the ctf version inside the ringbuffer header and perofming
introspection at the consumer level and split based on the value. This
was simply easier to do since we have all the data available at hand.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Change-Id: I4d12692fe2cab8ad9bf22db9b1d455ec397fa843