lib/classes/Variables.js/Variables/getValueFromSls
class Variables:  getValueFromSls(variableString) {
    let valueToPopulate = {};
    const requestedSlsVar = variableString.split(':')[1];
    if (requestedSlsVar === 'instanceId') {
      valueToPopulate = this.serverless.instanceId;
    }
    return BbPromise.resolve(valueToPopulate);
  }