cgroup.c: check return value of unit_realize_cgroup_now()

do not recurse further, if unit_realize_cgroup_now() failed
nspawn: trivial simplification
blkio: fix incorrect setting of cpu_shares

We should set up blockio_weight not cpu_shares.
udev: fix printf(3) type specifier

src/udev/udev-rules.c: In function 'add_rule':
src/udev/udev-rules.c:1078:33: warning: format '%lu' expects argument of type 'long unsigned int', but argument 8 has type 'int' [-Wformat=]
                                 log_error("invalid key/value pair in file %s on line %u,"
                                 ^
man: make reference to bind(2) explicit
"-" prefix for InaccessibleDirectories and ReadOnlyDirectories
zsh_completion: Fix single letter args

Things like -n to specify the lines to show with systemctl and
journalctl accepts syntax like:

  journalctl -n4
  systemctl -n14

Previously, typing `-nXX <tab>` where XX is a number, zsh would try to
complete an integer. Now it will see the XX and use the _journalctl_none
completion. This is also how any of the single letter options that take
arguments work as well.