thermal plugin: fixed value submitting

Signed-off-by: Markus Knetschke <markus.knetschke@gmail.com>
Signed-off-by: Florian Forster <octo@collectd.org>
thermal plugin: set the hostname

Signed-off-by: Markus Knetschke <markus.knetschke@gmail.com>
Signed-off-by: Florian Forster <octo@collectd.org>