util-lib: Don't propagate EACCES from find_binary PATH lookup to caller

util-lib: Don't propagate EACCES from find_binary PATH lookup to caller

On one of my test machines, test-path-util was failing because the
find_binary("xxxx-xxxx") was returning -EACCES instead of -ENOENT. This
happens because the PATH entry on that host contains a directory which
the user in question doesn't have access to. Typically applications
ignore permission errors when searching through PATH, for example in
bash:

    $ whoami
    cdown
    $ PATH=/root:/bin type sh
    sh is /bin/sh

This behaviour is present on zsh and other shells as well, though. This
patch brings our PATH search behaviour closer to other major Unix tools.