Implemented Flush() for httpd.responseLogger

[Jackkoz]

This pull request is a solution to issue "Empty respones from server when using chunked responses" that I have reported myself. It is a simple implementation of a missing method in httpd.responseLogger.

[Jackkoz]

Link to the mentioned issue: #2466

[otoolep]

Thanks @Jackkoz -- can you please sign the CLA?

http://influxdb.com/community/cla.html

[Jackkoz]

@otoolep - I've just signed it.

[otoolep]

Thanks @Jackkoz -- I have confirmed that the issue exists, and that this change fixes it.

[otoolep]

@corylanou

We do have a chunked query test here, but it's obviously not checking all behaviour.

https://github.com/influxdb/influxdb/blob/master/httpd/handler_test.go#L1658

[corylanou]

@otoolep I was just looking through tests for that exact thing :-). We should just open an issue to enhance that test to check for this if we want to close this. I agree this is a bug and the fix is correct.

+1

[otoolep]

I am digging into the code now -- what is about the code path the tests take that don't catch this?

[Jackkoz]

Have you tried checking if the tests turn off logging or use gzipped responses?

[otoolep]

We'll need to look into the testing, but merging this now.