frontend: perform argument value validation only on server
    
    Do not validate values of command arguments on the client and let the
    server handle validation.
    
    This will make the client more lightweight by not having it to carry
    validation code and metadata with itself for the price of increasing
    network traffic in case the validation fails.
    
    Types of the arguments are still validated on both the client and the
    server.
    
    https://fedorahosted.org/freeipa/ticket/4739
    
    Reviewed-By: David Kupka <dkupka@redhat.com>