This allows people to chroot sslh into a path to further harden it.
We have to rework the user logic a bit because we need to look up
the user details *before* we chroot (as we need to read /etc/passwd
files), but do the actual priv dropping *after* we chroot (so we
have permission to make the actual chroot call).
Similarly, we need to open the syslog before we drop privs because
/dev/log won't be available inside the chroot.
