XD-549 Add 'display' command for RichGauge
     - Display string representation of richgauge metric values
    (example: name: r1, value: 15.0, avg: 12.5, max: 15.0, min: 10.0)
  Added richgauge tests
     - Added AbstractMetricIntegrationTest that has metric specific helper methods
     - Fixed tests that use metric methods