Ensure contents of install dir are owned by root

/cc @irvingpop @lamont-granquist @opscode/engineering-leads @pburkholder 

This change will be cherry-picked into release/chefdk-0.2.2 also.

So theoretically since this seems to happen after we do the installation, a lower-privileged process could gain access to this directory before we `chown` it. Not sure if they could do a lot of damage before we fix the permissions, but if there's any non-zero time window where an attacker could elevate privileges or otherwise exercise unauthorized access, we should find a way to close that hole.