Use http.NewRequestWithContext for outgoing HTTP requests

This simple change mainly affects the distribution client. By respecting
the context the caller passes in, timeouts and cancellations will work
as expected. Also, transports which rely on the context (such as tracing
transports that retrieve a span from the context) will work properly.

Signed-off-by: Aaron Lehmann <alehmann@netflix.com>

registry/client/blob_writer_test.go

@@ -2,6 +2,7 @@ package client
 
 import (
 	"bytes"
+	"context"
 	"fmt"
 	"net/http"
 	"testing"
@@ -126,6 +127,7 @@ func TestUploadReadFrom(t *testing.T) {
 	defer c()
 
 	blobUpload := &httpBlobUpload{
+		ctx:    context.Background(),
 		client: &http.Client{},
 	}
 
@@ -265,6 +267,7 @@ func TestUploadSize(t *testing.T) {
 
 	// Writing with ReadFrom
 	blobUpload := &httpBlobUpload{
+		ctx:      context.Background(),
 		client:   &http.Client{},
 		location: e + readFromLocationPath,
 	}
@@ -284,6 +287,7 @@ func TestUploadSize(t *testing.T) {
 
 	// Writing with Write
 	blobUpload = &httpBlobUpload{
+		ctx:      context.Background(),
 		client:   &http.Client{},
 		location: e + writeLocationPath,
 	}
@@ -409,6 +413,7 @@ func TestUploadWrite(t *testing.T) {
 	defer c()
 
 	blobUpload := &httpBlobUpload{
+		ctx:    context.Background(),
 		client: &http.Client{},
 	}