fix SwaggerResponse for Swagger 2.0 objects
allowMultiple

in 1.2, either single value or array would be accepted by
allowMultiple, now only array would be accepted.
minor fixes

- make sure consumes/produces are [] not None
instead of replace $ref with real objects

we should keep $ref for tracing bugs, add another field 'ref_obj' to
keep real objects.
fixes
make jp_append tolorent on None
fixes
'void' means no response
rename test_schema to test_spec

schema is an object in swagger 2.0, so we better avoid use this name to
represent other things.