During working on #150837 I discovered that `google-oslogin` test
started failing, and so did some of my development machines. Turns out
it was because nscd doesn't start by default; rather it's wanted by
NSS lookup targets, which are not always fired up.
To quote from section on systemd.special(7) on `nss-user-lookup.target`:
> All services which provide parts of the user/group database should be
> ordered before this target, and pull it in.
Following this advice and comparing our unit to official `sssd.service`
unit (which is a similar service), we now pull NSS lookup targets from
the service, while starting it with `multi-user.target`.
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