systemctl: resolve symlinks when finding unit paths (#4545)
Otherwise we think the alias is the real unit, and may edit/cat the
wrong unit.
Before this patch:
$ systemctl edit autovt@ # creates dropin in /etc/systemd/system/autovt@.service.d
$ systemctl cat autovt@ | grep @.service
# /lib/systemd/system/autovt@.service
# that serial gettys are covered by serial-getty@.service, not this
# /etc/systemd/system/autovt@.service.d/override.conf
$ systemctl cat getty@ | grep @.service
# /lib/systemd/system/getty@.service
# that serial gettys are covered by serial-getty@.service, not this
After this patch
$ systemctl edit autovt@ # creates dropin in /etc/systemd/system/getty@.service.d
$ systemctl cat autovt@ | grep @.service
# /usr/lib/systemd/system/getty@.service
# that serial gettys are covered by serial-getty@.service, not this
# /etc/systemd/system/getty@.service.d/override.conf
systemctl cat getty@ | grep @.service
# /usr/lib/systemd/system/getty@.service
# that serial gettys are covered by serial-getty@.service, not this
# /etc/systemd/system/getty@.service.d/override.conf