Defaults in dummyserver will fail to decode on Python3

[reversefold]

I found this while working on #1257

Most of the defaults given to request.params.get() are strings rather than bytes. Some of these then have decode() called on them, which fails as you can only decode bytes, not strings. These function work fine if a value is passed in but if no value is passed in they will error out with

AttributeError: 'str' object has no attribute 'decode'