add 'sudo' for chef-server-ctl test on server install docs

Because it fails with:

    smith@chef:~$ chef-server-ctl test
    /opt/chef-server/embedded/service/chef-pedant/lib/pedant/config.rb:34:in `from_argv': Configuration file '/var/opt/chef-server/chef-pedant/etc/pedant_config.rb' not found! (RuntimeError)
            from /opt/chef-server/embedded/service/chef-pedant/lib/pedant.rb:44:in `setup'
            from ./bin/chef-pedant:26:in `<main>'

if you don't use sudo.