Add context to all http.NewRequest #3257

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

backend/googlecloudstorage/googlecloudstorage.go

@@ -1007,6 +1007,7 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.Read
 	if err != nil {
 		return nil, err
 	}
+	req = req.WithContext(ctx) // go1.13 can use NewRequestWithContext
 	fs.FixRangeOption(options, o.bytes)
 	fs.OpenOptionAddHTTPHeaders(req.Header, options)
 	var res *http.Response