Split-out request of failed units from systemd into a separate member
function.
This increases the readability and extendability, but preserves the
current functionality (non-functional change).
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>
