message: [bugfix] fix metrics/metric control default
  We should pick an arbitrary metric by default. This broke when
  improving the metrics selector recently.
diff: @@ -63,8 +63,7 @@ export const controls = {
  valueKey: 'metric_name',
  optionRenderer: m => <MetricOption metric={m} />,
  valueRenderer: m => <MetricOption metric={m} />,
  - default: control =>
  - control.choices && control.choices.length > 0 ? [control.choices[0][0]] : null,
  + default: c => c.options && c.options.length > 0 ? [c.options[0].metric_name] : null,
  mapStateToProps: state => ({
  options: (state.datasource) ? state.datasource.metrics : [],
  }),
  @@ -100,9 +99,8 @@ export const controls = {
  validators: [v.nonEmpty],
  optionRenderer: m => <MetricOption metric={m} />,
  valueRenderer: m => <MetricOption metric={m} />,
  + default: c => c.options && c.options.length > 0 ? c.options[0].metric_name : null,
  valueKey: 'metric_name',
  - default: control =>
  - control.choices && control.choices.length > 0 ? control.choices[0][0] : null,
  mapStateToProps: state => ({
  options: (state.datasource) ? state.datasource.metrics : [],
  }),
  