Add HashiCorp Nomad provider (#483)

* provider: adding Nomad provider

* updating CONTRIBUTING.md with Nomad provider

* updated README.md by adding the Nomad provider

* fix typo

* adding nomad/api and nomad/testutil deps

* adding Nomad binary dependency for provider tests

* fixed the nomad binary download command step and added tolerations to the nomad provider.

* adding nomad provider demo gif

* adding my name to authors

* adding two missing go-rootcerts files after dep ensure

* delete pod comment

vendor/github.com/armon/go-metrics/inmem_endpoint.go

@@ -0,0 +1,118 @@
+package metrics
+
+import (
+	"fmt"
+	"net/http"
+	"sort"
+	"time"
+)
+
+// MetricsSummary holds a roll-up of metrics info for a given interval
+type MetricsSummary struct {
+	Timestamp string
+	Gauges    []GaugeValue
+	Points    []PointValue
+	Counters  []SampledValue
+	Samples   []SampledValue
+}
+
+type GaugeValue struct {
+	Name  string
+	Hash  string `json:"-"`
+	Value float32
+
+	Labels        []Label           `json:"-"`
+	DisplayLabels map[string]string `json:"Labels"`
+}
+
+type PointValue struct {
+	Name   string
+	Points []float32
+}
+
+type SampledValue struct {
+	Name string
+	Hash string `json:"-"`
+	*AggregateSample
+	Mean   float64
+	Stddev float64
+
+	Labels        []Label           `json:"-"`
+	DisplayLabels map[string]string `json:"Labels"`
+}
+
+// DisplayMetrics returns a summary of the metrics from the most recent finished interval.
+func (i *InmemSink) DisplayMetrics(resp http.ResponseWriter, req *http.Request) (interface{}, error) {
+	data := i.Data()
+
+	var interval *IntervalMetrics
+	n := len(data)
+	switch {
+	case n == 0:
+		return nil, fmt.Errorf("no metric intervals have been initialized yet")
+	case n == 1:
+		// Show the current interval if it's all we have
+		interval = i.intervals[0]
+	default:
+		// Show the most recent finished interval if we have one
+		interval = i.intervals[n-2]
+	}
+
+	summary := MetricsSummary{
+		Timestamp: interval.Interval.Round(time.Second).UTC().String(),
+		Gauges:    make([]GaugeValue, 0, len(interval.Gauges)),
+		Points:    make([]PointValue, 0, len(interval.Points)),
+	}
+
+	// Format and sort the output of each metric type, so it gets displayed in a
+	// deterministic order.
+	for name, points := range interval.Points {
+		summary.Points = append(summary.Points, PointValue{name, points})
+	}
+	sort.Slice(summary.Points, func(i, j int) bool {
+		return summary.Points[i].Name < summary.Points[j].Name
+	})
+
+	for hash, value := range interval.Gauges {
+		value.Hash = hash
+		value.DisplayLabels = make(map[string]string)
+		for _, label := range value.Labels {
+			value.DisplayLabels[label.Name] = label.Value
+		}
+		value.Labels = nil
+
+		summary.Gauges = append(summary.Gauges, value)
+	}
+	sort.Slice(summary.Gauges, func(i, j int) bool {
+		return summary.Gauges[i].Hash < summary.Gauges[j].Hash
+	})
+
+	summary.Counters = formatSamples(interval.Counters)
+	summary.Samples = formatSamples(interval.Samples)
+
+	return summary, nil
+}
+
+func formatSamples(source map[string]SampledValue) []SampledValue {
+	output := make([]SampledValue, 0, len(source))
+	for hash, sample := range source {
+		displayLabels := make(map[string]string)
+		for _, label := range sample.Labels {
+			displayLabels[label.Name] = label.Value
+		}
+
+		output = append(output, SampledValue{
+			Name:            sample.Name,
+			Hash:            hash,
+			AggregateSample: sample.AggregateSample,
+			Mean:            sample.AggregateSample.Mean(),
+			Stddev:          sample.AggregateSample.Stddev(),
+			DisplayLabels:   displayLabels,
+		})
+	}
+	sort.Slice(output, func(i, j int) bool {
+		return output[i].Hash < output[j].Hash
+	})
+
+	return output
+}