Permission denied when using named volume for loki storage

[Mario-Hofstaetter]

Describe the bug
When using a named docker volume to persist data for directory: /tmp/loki loki fails to start with

level=error ts=2020-03-22T18:16:33.326631457Z caller=log.go:141 msg="error initializing bucket client" err="mkdir /tmp/loki/chunks: permission denied"

This is not the case with image grafana/loki:v1.3.0, because the USER changed recently:
45b51ef#diff-0d3766d51f4b0ce5183c885a65c6045b

To Reproduce
On any docker host (e.g. https://labs.play-with-docker.com) run:

• wget https://gist.githubusercontent.com/Mario-Hofstaetter/184376e4449aa25733c286f9659dedcf/raw/a7ddb12495a37bd2228913510a430a24670af271/docker-compose.yml
  this has been edited from /master/cmd/loki/loki-local-config.yaml
• Run docker-compose up loki

Expected behavior
Loki should able to use a named volume to persist data, at least for the default data directory.

Environment:

• docker, image grafana/loki:latest (id /master/cmd/loki/loki-local-config.yaml)

Suggested Solution
This can be fixed by creating /tmp/loki and setting permissions in Dockerfile.
But /tmp/loki is a poor choice for the persistent data directory.

• Change directory for lokal storage_config to /loki/
• Set permissions for /loki/ and /etc/loki/

[Depechie]

Although this name change is ok, Tempo never had a problem with creating /wal and /blocks subfolders in /tmp/tempo and is still using /tmp naming.
Would be nice all grafana tools use the same setup for docker ( docker-compose ).