Add the ability to lookup usernames and check uids. Bails out early if the given
uid/name does not exist and avoids using atoi() (which is bad because we can't
tell if it parsed an int or a pumpkin).
Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>