hostnamectl: Exit with zero on success

In show_all_names(), bus_map_all_properties() returns 1 on success which is
then used as the return code of show_all_names() and eventually main(). Exit
with zero in main() on all nonnegative results to guard against similar errors.
treewide: more log_*_errno() conversions, multiline calls

Basically:

find . -name '*.[ch]' | while read f; do perl -i.mmm -e \
'local $/;
 local $_=<>;
 s/log_(debug|info|notice|warning|error|emergency)\("([^"]*)%s"([^;]*),\s*strerror\(-?([->a-zA-Z_]+)\)\);/log_\1_errno(\4, "\2%m"\3);/gms;print;' \
 $f; done

Plus manual indentation fixups.