Replace pipeline stage in docker driver

[andoks]

Is your feature request related to a problem? Please describe.
I am using the docker driver to consume postgresql logs, and I would like to rewrite postgresql's levels to more standard ones using the replace stage, but it seems like the replace stage does not work when configured as a pipeline stage with the loki driver.

Describe the solution you'd like
The replace pipeline stage in the docker driver too

Describe alternatives you've considered
None

Additional context
Loki driver info (docker plugin inspect loki)

[
    {
        "Config": {
            "Args": {
                "Description": "",
                "Name": "",
                "Settable": null,
                "Value": null
            },
            "Description": "Loki Logging Driver",
            "DockerVersion": "17.09.0-ce",
            "Documentation": "https://github.com/grafana/loki",
            "Entrypoint": [
                "/bin/docker-driver"
            ],
            "Env": [
                {
                    "Description": "Set log level to output for plugin logs",
                    "Name": "LOG_LEVEL",
                    "Settable": [
                        "value"
                    ],
                    "Value": "info"
                }
            ],
            "Interface": {
                "Socket": "loki.sock",
                "Types": [
                    "docker.logdriver/1.0"
                ]
            },
            "IpcHost": false,
            "Linux": {
                "AllowAllDevices": false,
                "Capabilities": null,
                "Devices": null
            },
            "Mounts": [
                {
                    "Description": "Optional external pipeline files",
                    "Destination": "/data",
                    "Name": "data",
                    "Options": [
                        "bind",
                        "ro"
                    ],
                    "Settable": [
                        "source",
                        "destination"
                    ],
                    "Source": "",
                    "Type": "none"
                }
            ],
            "Network": {
                "Type": "host"
            },
            "PidHost": false,
            "PropagatedMount": "",
            "User": {},
            "WorkDir": "",
            "rootfs": {
                "diff_ids": [
                    "sha256:b5a05d3a388293d9280239ff690aa8ff0b77586b690bc67ba88bef7a9994e098"
                ],
                "type": "layers"
            }
        },
        "Enabled": true,
        "Id": "1bbb0f13f71bcfad75af8dad94f506ae78b99fd86832f7d3d268f800f42c9267",
        "Name": "loki:latest",
        "PluginReference": "docker.io/grafana/loki-docker-driver:master-afd3daf",
        "Settings": {
            "Args": [],
            "Devices": [],
            "Env": [
                "LOG_LEVEL=info"
            ],
            "Mounts": [
                {
                    "Description": "Optional external pipeline files",
                    "Destination": "/data",
                    "Name": "data",
                    "Options": [
                        "bind",
                        "ro"
                    ],
                    "Settable": [
                        "source",
                        "destination"
                    ],
                    "Source": "",
                    "Type": "none"
                }
            ]
        }
    }
]

Logging configuration I use

 logging:                                                                                               
            driver: loki                                                                                       
            options:                                                                                           
                loki-url: *loki-url                                                                            
                loki-pipeline-stages: |                                                                        
                    - regex:                                                                                   
                        expression: ^(?P<timestamp>\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}\.\d{3} \w+) \[\d+\] (?P<level>\w+)                                                                                                     
                    - labels:                                                                                  
                        internal_level: level                                                                  
                        level: level                                                                           
                    - replace:                                                                                 
                        expression: "(\\S+)"                                                                   
                        source: "level"                                                                        
                        replace: "info"                                                                        
                    - timestamp:                                                                               
                        source: timestamp                                                                      
                        format: 2006-01-02 15:04:05.999 MST          

#2033
https://github.com/grafana/loki/tree/master/cmd/docker-driver#pipeline-stages

[andoks]

This was a PEBCAK, and replace is working in the loki driver too.

The issue was that the labels stage must run after the replace stage.