Fixed missed static check issue. (#1309)

Signed-off-by: Bartek Plotka <bwplotka@gmail.com>

cmd/thanos/sidecar.go

@@ -20,15 +20,17 @@ import (
 	"github.com/improbable-eng/thanos/pkg/store"
 	"github.com/improbable-eng/thanos/pkg/store/storepb"
 	"github.com/oklog/run"
-	"github.com/opentracing/opentracing-go"
+	opentracing "github.com/opentracing/opentracing-go"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/tsdb/labels"
 	"google.golang.org/grpc"
-	"gopkg.in/alecthomas/kingpin.v2"
+	kingpin "gopkg.in/alecthomas/kingpin.v2"
 )
 
+const waitForExternalLabelsTimeout = 10 * time.Minute
+
 func registerSidecar(m map[string]setupFunc, app *kingpin.Application, name string) {
 	cmd := app.Command(name, "sidecar for Prometheus server")
 
@@ -248,15 +250,16 @@ func runSidecar(
 		g.Add(func() error {
 			defer runutil.CloseWithLogOnErr(logger, bkt, "bucket client")
 
-			extLabelsTimeout := 10 * time.Minute
-			extLabelsCtx, _ := context.WithTimeout(ctx, extLabelsTimeout)
+			extLabelsCtx, cancel := context.WithTimeout(ctx, waitForExternalLabelsTimeout)
+			defer cancel()
+
 			if err := runutil.Retry(2*time.Second, extLabelsCtx.Done(), func() error {
 				if len(m.Labels()) == 0 {
 					return errors.New("not uploading as no external labels are configured yet - is Prometheus healthy/reachable?")
 				}
 				return nil
 			}); err != nil {
-				return errors.Wrapf(err, "aborting as no external labels found after waiting %s", extLabelsTimeout)
+				return errors.Wrapf(err, "aborting as no external labels found after waiting %s", waitForExternalLabelsTimeout)
 			}
 
 			var s *shipper.Shipper