Turn off hash merge, add gh_user_no_sudo

add users without sudo (gh_user_no_sudo)
    
It's handy to be able to create users that *don't* have sudo rights. Here at Stanford we use this to add users to our VPC bastion box (ssh proxy) so these users can use this machine for ssh tunneling, but I don't want to give those users the keys to the kingdom.
    
This let's me configure a playbook like this.
    
       roles:
         - common
         - supervisor
         - role: gh_users
           gh_users:
             - su1
             - su2
             - su3
           gh_users_no_sudo:
             - normal1
             - normal2
    
The new gh_users_no_sudo list can be empty.

@jbau or @jrbl.