sulogin-shell: do daemon-reload before starting default target

sulogin-shell: do daemon-reload before starting default target

If the user modifies configuration, e.g. /etc/fstab, they might forget to tell
systemd about the changes. Let's do a reload for them.

Note that doing a reload should be safe, because emergency and rescue modes are
"single threaded" and nothing should be doing changes at the point where we are
exiting from the sushell. Also, daemon-reload can be implicitly called at
various moments, so we can ignore the case where the user did some incompatible
changes on disk and is counting on systemd never reloading and picking them up.

C.f. #7565.