ipatests: Add test cases for subdomain users on legacy clients
    
    Adds test cases for:
    * getent subdomain user on legacy client
    * getent subdomain group on legacy client
    * getent id subdomain user on legacy client
    * ssh into legacy client with subdomain user
    * ssh into legacy client with disabled subdomain user
    
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>