Fix: add missing pthread_join in sessiond

Signed-off-by: David Goulet <dgoulet@efficios.com>
[HEAD MERGE] Add -j/--jul to lttng UI and ABI

The JUL domain is set as unsupported in the session daemon so only the
client side is implemented.

Signed-off-by: David Goulet <dgoulet@efficios.com>
[HEAD MERGE] Add jul.c/.h to sessiond code

The JUL domain is added to a ust session and created/destroyed in the
trace-ust.c API.

Signed-off-by: David Goulet <dgoulet@efficios.com>
[HEAD MERGE] Add JUL registration thread

Listening on port 5345 by default and adds the --jul-tcp-port option to
the session daemon command line options.

At this commit, the thread is started and listening for incoming
registration but they are not handled.

Signed-off-by: David Goulet <dgoulet@efficios.com>