systemd-systemctl: fix instance template WantedBy symlink construction

systemd-systemctl: fix instance template WantedBy symlink construction

Fix issue of the below instance template systemd service dependency

[Install]
WantedBy=svc-wants@%i.service

creating the symlink (instance "a" example)

/etc/systemd/system/svc-wants@%i.service.wants/svc-wanted-by@a.service

which should be

/etc/systemd/system/svc-wants@a.service.wants/svc-wanted-by@a.service

as implemented by this change.

The functionality appears regressed just after "thud" baseline when the
logic was refactored from shell script into python (commit
925e30cb104ece7bfa48b78144e758a46dc9ec3f)

(From OE-Core rev: 308397f0bb3d6f3d4e9ec2c6a10823184049c9b5)

Signed-off-by: Martin Siegumfeldt <mns@gomspace.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
(cherry picked from commit 372b29c8ad270d4d430c26a4e614976c7029afaf)
Signed-off-by: Steve Sakoman <steve@sakoman.com>