The mosquitto runtime test can randomly fail on slow
runners, see [1].
This commit improves this test in the following ways:
- the mosquitto_sub subscriber process is now started in a subshell
to suppress the job control messages (to prevent any spurious
messages when the job stops),
- the standard error is redirected to /dev/null, to prevent the
printing of any messages,
- the mosquitto_pub publisher process is started later, by increasing
the sleep time,
- finally, a new sleep time is introduced between the mosquitto_pub
publisher process and the check of the mosquitto_sub subscriber, to
make sure it will have time to write its output and exit.
Fixes: [1]
[1] https://gitlab.com/buildroot.org/buildroot/-/jobs/8453386454
Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
