Make tracing interface to coalesce logging/tracing (#519)

* Define and use an interface for logging.

This allows alternative implementations to use whatever logging package
they want.

Currently the interface just mimicks what logrus already implements,
with minor modifications to not rely on logrus itself. I think the
interface is pretty solid in terms of logging implementations being able
to do what they need to.

* Make tracing interface to coalesce logging/tracing

Allows us to share data between the tracer and the logger so we can
simplify log/trace handling wher we generally want data to go both
places.

vkubelet/apiserver.go

@@ -3,7 +3,6 @@ package vkubelet
 import (
 	"net/http"
 
-	"github.com/Sirupsen/logrus"
 	"github.com/gorilla/mux"
 	"github.com/virtual-kubelet/virtual-kubelet/log"
 	"github.com/virtual-kubelet/virtual-kubelet/providers"
@@ -73,7 +72,7 @@ func AttachMetricsRoutes(p providers.Provider, mux ServeMux) {
 
 func instrumentRequest(r *http.Request) *http.Request {
 	ctx := r.Context()
-	logger := log.G(ctx).WithFields(logrus.Fields{
+	logger := log.G(ctx).WithFields(log.Fields{
 		"uri":  r.RequestURI,
 		"vars": mux.Vars(r),
 	})
@@ -96,14 +95,12 @@ func InstrumentHandler(h http.Handler) http.Handler {
 
 // NotFound provides a handler for cases where the requested endpoint doesn't exist
 func NotFound(w http.ResponseWriter, r *http.Request) {
-	logger := log.G(r.Context())
-	log.Trace(logger, "404 request not found")
+	log.G(r.Context()).Debug("404 request not found")
 	http.Error(w, "404 request not found", http.StatusNotFound)
 }
 
 // NotImplemented provides a handler for cases where a provider does not implement a given API
 func NotImplemented(w http.ResponseWriter, r *http.Request) {
-	logger := log.G(r.Context())
-	log.Trace(logger, "501 not implemented")
+	log.G(r.Context()).Debug("501 not implemented")
 	http.Error(w, "501 not implemented", http.StatusNotImplemented)
 }