Use logrus to logging in docker plugin

[IzabellaRaulin]

More logs to trace collection process are needed but they should be depended on the set log level. Such logs should have fields with full information what happens, for example:

logrus.WithFields(logrus.Fields{
    "_block": "GetStatsFromContainer",
    "_id": container_id,
}).Info("Getting stats from docker container")

It will be helpful for debug purpose.