code: function buildParams (identifier, instanceState) {
    var params = {}
  
    if (instanceState) {
      params.Filters = [
        {
          Name: 'instance-state-name',
          Values: [instanceState]
        }
      ]
    }
  
    if (isInstanceId(identifier)) {
      params.InstanceIds = [identifier]
      return params
    }
  
    params.Filters = params.Filters || []
  
    params.Filters.push({
      Name: 'tag:Name',
      Values: [identifier]
    })
  
    return params
  }
docs: Builds the correct set of params depending on whether or not the
  identifier is an instanceId or a name.
  
  @param {state} instanceState
  @param {string} identifier
  @returns {object} params for the ec2.describeInstances call.