tracing: support dynamic reloading, more aggressive envoy restart (#2262)

* tracing: support dynamic reloading, more aggressive envoy restart

* set exporter to nil

* actually register tracer

internal/telemetry/trace/jaeger.go

@@ -0,0 +1,37 @@
+package trace
+
+import (
+	"contrib.go.opencensus.io/exporter/jaeger"
+	octrace "go.opencensus.io/trace"
+)
+
+type jaegerProvider struct {
+	exporter *jaeger.Exporter
+}
+
+func (provider *jaegerProvider) Register(opts *TracingOptions) error {
+	jOpts := jaeger.Options{
+		ServiceName:   opts.Service,
+		AgentEndpoint: opts.JaegerAgentEndpoint,
+	}
+	if opts.JaegerCollectorEndpoint != nil {
+		jOpts.CollectorEndpoint = opts.JaegerCollectorEndpoint.String()
+	}
+	jex, err := jaeger.NewExporter(jOpts)
+	if err != nil {
+		return err
+	}
+	octrace.RegisterExporter(jex)
+	provider.exporter = jex
+	return nil
+}
+
+func (provider *jaegerProvider) Unregister() error {
+	if provider.exporter == nil {
+		return nil
+	}
+	octrace.UnregisterExporter(provider.exporter)
+	provider.exporter.Flush()
+	provider.exporter = nil
+	return nil
+}