Fix: send the streams sent message after metadata

We now make sure that we only sent the streams_sent message to the relay
when all the streams (including the metadata) are sent.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: notify the viewer if new streams got added

As soon as new streams are available, the viewer must start reading
them, otherwise we risk to ignore complete streams.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: handle new streams in live mode in relayd

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: code refactoring of viewer streams in relayd

This also renames the lttng-viewer.h to lttng-viewer-abi.h which
represents the live reading ABI.

Acked-by: Julien Desfossez <julien.desfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>