sync with Cortex v0.3.0-rc.0 and resolve conflict

[mizeng]

What this PR does / why we need it:
Sync with Cortex and fix conflict, so it will not break Loki build.

Which issue(s) this PR fixes:
Fixes #1033

Special notes for your reviewer:

Checklist

• Documentation added
• Tests updated

[mizeng]

@cyriltovena Could you help to review?

[mizeng]

what's CI go version? I see this error:

#!/bin/bash -eo pipefail
make BUILD_IN_CONTAINER=false test
>> writing assets
GOOS=linux go generate -x -v ./pkg/promtail/server/ui
pkg/promtail/server/ui/assets_vfsdata.go
pkg/promtail/server/ui/doc.go
go run -tags=dev assets_generate.go
writing assets_vfsdata.go
CGO_ENABLED=1 go build -ldflags "-s -w -X github.com/grafana/loki/vendor/github.com/prometheus/common/version.Branch=pull/1047 -X github.com/grafana/loki/vendor/github.com/prometheus/common/version.Version=pull-1047-75adaee -X github.com/grafana/loki/vendor/github.com/prometheus/common/version.Revision=75adaee2 -X github.com/grafana/loki/vendor/github.com/prometheus/common/version.BuildUser=root@7f45bd800e3d -X github.com/grafana/loki/vendor/github.com/prometheus/common/version.BuildDate=2019-09-24T01:24:56Z" -tags netgo -o cmd/promtail/promtail ./cmd/promtail
# github.com/grafana/loki/vendor/github.com/prometheus/prometheus/tsdb/goversion
vendor/github.com/prometheus/prometheus/tsdb/goversion/init.go:17:9: undefined: _SoftwareRequiresGOVERSION1_12

google showed it should be related to GO version under 1.12?

[cyriltovena]

@gouthamve is cortex using 1.12 now ?

[mizeng]

I think it is using go 1.13 now.. cortexproject/cortex@9d6c4d1

[cyriltovena]

We will have to wait for #1062

[mizeng]

@cyriltovena rebased with latest Loki code, could you plz help review again?

[cyriltovena]

I would prefer to wait for the final 0.3

[mizeng]

make sense

[cyriltovena]

0.3 is out @mizeng if you want to resume the work.

[mizeng]

@cyriltovena seems no need. Loki works well with Cortex v0.3.0, seems someone fixed the conflict.