Improve websocket support

[gyson]

Description

When using it with Apache Zeppelin (it requires websocket), it got 500 error with "WebSocket handshake: Unexpected response code: 500".

With some investigation, it's caused by lack support of http.Hijacker, it raised 500 error from here.

This PR added http.Hijacker support to responseLogger to resolve above issue.

There is one more nice to have change, which is to support value case insensitive for header Connection because nginx documented to use proxy_set_header Connection "upgrade" from here. The current implementation only accept Upgrade.

Motivation and Context

go version: v1.12

Using it with Apache Zeppelin, it got 500 error with "WebSocket handshake: Unexpected response code: 500".

How Has This Been Tested?

• added unit test
• tested change in my Apache Zeppelin setup, webscoket works properly after this change.

Checklist:

• My change requires a change to the documentation or CHANGELOG.
• I have updated the documentation/CHANGELOG accordingly.
• I have created a feature (non-master) branch for my PR.

[ploxiln]

looks good to me

[JoelSpeed]

This is great, thanks! 😄