RollerProvider = function(_mongoose, _TaskMdl) {
  mongoose = _mongoose;
  TaskMdl = _TaskMdl;
  dbUtils = require("./utils/db.utils")(mongoose);
  getModel = dbUtils.getModel;
  getCollectionForStep = dbUtils.getCollectionForStep;

  return Roller;
}
Initializes variables and gets the roller.

@param _mongoose the mongoose instance
@param _TaskMdl the task model

@returns An object containing rollback functions
@constructor