collectd: run sensors-detect in background

collectd: run sensors-detect in background

on some machines the i2c sensor search take very long time
which cause hang at first boot.

Now the search is started in background and waited for max one
minute before continue load of collectd.
On such machines collectd will not get all sensors at first startup.

fixes #12329

Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>
Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>