Refactor querier http error handling.

[cyriltovena]

Signed-off-by: Cyril Tovena cyril.tovena@gmail.com

This ensure we return proper status code depending on the error in the querier.

I'll send another PR to also update the frontend from cortex which has a similar change.

[slim-bean]

LGTM

[codecov-io]

Codecov Report

Merging #1745 into master will increase coverage by 0.17%.
The diff coverage is 41.17%.

@@            Coverage Diff             @@
##           master    #1745      +/-   ##
==========================================
+ Coverage    64.2%   64.38%   +0.17%     
==========================================
  Files         121      121              
  Lines        9085     9080       -5     
==========================================
+ Hits         5833     5846      +13     
+ Misses       2848     2832      -16     
+ Partials      404      402       -2

Impacted Files	Coverage Δ
pkg/querier/http.go	11.17% <41.17%> (+4.43%)	⬆️
pkg/ingester/transfer.go	65% <0%> (-1.43%)	⬇️
pkg/promtail/targets/filetarget.go	70.55% <0%> (+1.84%)	⬆️
pkg/promtail/targets/tailer.go	78.16% <0%> (+4.59%)	⬆️