Checking for the availability of a given proxy member can be done in the
lambda function as well.
Signed-off-by: Steffen Kothe <steffen.kothe@skothe.net>
Keeping nr_failed as member allows to split-out calculation of overall
failed units into updateData.
Signed-off-by: Steffen Kothe <steffen.kothe@skothe.net>
Slim images of Debian tend to be smaller even during development. Hence
replace the full-fledged variant with the slim one.
Signed-off-by: Steffen Kothe <steffen.kothe@skothe.net>