fn: stats view/distribution improvements (#1154)

* fn: stats view/distribution improvements

*) View latency distribution is now an argument
in view creation functions. This allows easier
override to set custom buckets. It is simplistic
and assumes all latency views would use the same
set, but in practice this is already the case.
*) Removed API view creation to main, this should not
be enabled for all node types. This is consistent with
the rest of the system.

* fn: Docker samples of cpu/mem/disk with specific buckets

api/common/stats_utils.go

@@ -0,0 +1,34 @@
+package common
+
+import (
+	"github.com/sirupsen/logrus"
+	"go.opencensus.io/stats"
+	"go.opencensus.io/stats/view"
+	"go.opencensus.io/tag"
+)
+
+func CreateView(measure stats.Measure, agg *view.Aggregation, tagKeys []string) *view.View {
+	return &view.View{
+		Name:        measure.Name(),
+		Description: measure.Description(),
+		Measure:     measure,
+		TagKeys:     makeKeys(tagKeys),
+		Aggregation: agg,
+	}
+}
+
+func MakeMeasure(name string, desc string, unit string) *stats.Int64Measure {
+	return stats.Int64(name, desc, unit)
+}
+
+func makeKeys(names []string) []tag.Key {
+	tagKeys := make([]tag.Key, len(names))
+	for i, name := range names {
+		key, err := tag.NewKey(name)
+		if err != nil {
+			logrus.Fatal(err)
+		}
+		tagKeys[i] = key
+	}
+	return tagKeys
+}