bin/install-qa-check.d: add new 90bad-bin-owner QA check.

System executables that are not owned by root pose a security
risk. The owner of the executable is free to modify it at any time;
so, for example, he can change a daemon's behavior to make it
malicious before the next time the service is started (usually by
root).

On a "normal" system, the superuser should own every system executable
(even setuid ones, for security reasons). This commit adds a new
install-time check that reports any such binaries with a QA
warning. To avoid false positives, non-"normal" systems (like prefix)
are skipped at the moment.

Bug: https://bugs.gentoo.org/629398
1 file changed