Http Channel does not handle 204 response gracefully

[jamime]

Expected behavior

The remote.html runner should report a success when it receives a 204 from intern

Current behavior

Errors are reported in the browser window such as Error sending testStart/testEnd. The results are reported to the intern process correctly.

Possible solution

When lib/middleware/post.ts returns a 204 we should not try to parse the empty body.

intern/src/lib/channels/Http.ts

Line 79 in f56177f

return response.json<any[]>();

Steps to reproduce (for bugs)

You need to disable the websocket connection by setting "socketPort": false in your config.

Environment

Intern version: 4.1.5
Node version: v9.7.1
NPM version: 5.6.0
Browser version: Chrome 65

Additional information

whatwg/fetch#113

[jason0x43]

This is included in Intern 4.2.0.