Add support for tracing via OpenCencus

This adds a few flags for configuring the tracer.
Includes support for jaeger tracing (built into OC).

providers/azure/client/aci/client.go

@@ -4,6 +4,10 @@ import (
 	"fmt"
 	"net/http"
 
+	"go.opencensus.io/plugin/ochttp/propagation/b3"
+
+	"go.opencensus.io/plugin/ochttp"
+
 	azure "github.com/virtual-kubelet/virtual-kubelet/providers/azure/client"
 )
 
@@ -40,6 +44,12 @@ func NewClient(auth *azure.Authentication) (*Client, error) {
 	if err != nil {
 		return nil, fmt.Errorf("Creating Azure client failed: %v", err)
 	}
+	hc := client.HTTPClient
+	hc.Transport = &ochttp.Transport{
+		Base:           hc.Transport,
+		Propagation:    &b3.HTTPFormat{},
+		NewClientTrace: ochttp.NewSpanAnnotatingClientTrace,
+	}
 
 	return &Client{hc: client.HTTPClient, auth: auth}, nil
 }