Default value and is_required not appropriately interacting

[schrockn]

If a scalar field gets a default value, it should not be considered required since in the absence

for example:

    @solid(config_schema={'default_to_one': Field(int, default_value=1)})
    def return_default_to_one(context):
        return context.solid_config['default_to_one']

    # This currently throws. It should not require configuration as the
    # the default value should make it *not* required.
    execute_solid(return_default_to_one)

This should work and the solid should return 1. It currently does not. I believes that it requires configuration.