Fix: quiet option is not set in sessiond-config

The quiet option is currently set directly while parsing the
command line options of the lttng-sessiond. Since it is not
set in the sessiond configuration object, its default value
(false) overwrites the lttng_opt_quiet option when the
configuration is applied.

Reported-by: Stanislav Vovk <stanislav.vovk@windriver.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>