lttng-tools: Allow reconnect to relayd

lttng-tools: Allow reconnect to relayd

If relayd is started after connection attempt from consumerd it will
leave the session in disconnected state and causes the following
inconvenience. This is covered by an upstream feature, see
https://bugs.lttng.org/issues/883. Before it's done, this patches
allows users to reconnect to relayd.

root@localhost:~# lttng enable-event --userspace --all
Error: Events: UST create channel failed (channel channel0, session trace_session)
root@localhost:~# lttng-relayd -b
Warning: No tracing group detected
root@localhost:~# lttng enable-event --userspace --all
Error: Events: UST create channel failed (channel channel0, session trace_session)

Signed-off-by: He Zhe <zhe.he@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>