* Docker blocks: Add loki blocks for loki releases

- Loki did major API changes between 0.3 and 0.4
- Adding blocks to simplify Grafana datasource testing for different
versions
- keeing `loki` block pointing at loki master
- Run all versions in parallel:
```
./create_docker_compose.sh loki0.3 loki0.4 loki
```
- all versions have different hostnames and ports internally
- datasource url depends on version so you can set them up as separate
datasources:
  - master: http://localhost:3100/
  - 0.3.0: http://localhost:3103/
  - 0.4.0: http://localhost:3104/

* Add loki minor version datasources