Add Error Case for /api/v0/setup within backend/handlers/setup/setuphandler_test.go

[pwdel]

• Within setuphandler_test.go we have a, "happy," test case which returns a 200.
• We would like to create a test case that returns 500, in the case that the API does not work for whatever reason, for the sake of completion of the test.
• This test case could be the same as the happy case, but use the http library to return an invalid HTTP response.
• I had previously had trouble building this, the intended 500 error kept returning 200 and I'm not sure what I was doing wrong, so I just skipped it and went with only the happy case. If anyone knows how to fix this please do.