Fix missing files in METALOG with -DNO_ROOT

[arichardson]

Summary

By using INSTALL_LINK instead of calling ln during install the files
end up in the METALOG file as well if we use -DNO_ROOT and will be
included in a disk image when using makefs with METALOG as the input.

Also added /var/db/services.db to METALOG for -DNO_ROOT

Test Plan

now all files in the rootfs are included in METALOG

[brooks]

LGTM