sd-bus: when showing brief message info show error name in debug out put too

sd-bus: when showing brief message info show error name in debug out put too

When debug logging is enabled we show brief information about every bus
message we send or receieve. Pretty much all information is shown,
except for the error name if a message is an error (interestingly we do
print the error text however). Fix that, and add the error name as well.