Add context to all http.NewRequest #3257

When we drop support for go1.12 we can use http.NewRequestWithContext

backend/s3/s3.go

@@ -1942,7 +1942,7 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 		if err != nil {
 			return errors.Wrap(err, "s3 upload: new request")
 		}
-		httpReq = httpReq.WithContext(ctx)
+		httpReq = httpReq.WithContext(ctx) // go1.13 can use NewRequestWithContext
 
 		// set the headers we signed and the length
 		httpReq.Header = headers