[errors] de-specialize Transient in favor of Tags.

buildbucket/client/cmd/buildbucket/client.go

Index: buildbucket/client/cmd/buildbucket/client.go
diff --git a/buildbucket/client/cmd/buildbucket/client.go b/buildbucket/client/cmd/buildbucket/client.go
index 64ca76a963bc8224c26886c87c643a72616d06da..4f2792c7f8e181b6f6c54a5acd901c82dbbcb5f6 100644
--- a/buildbucket/client/cmd/buildbucket/client.go
+++ b/buildbucket/client/cmd/buildbucket/client.go
@@ -15,7 +15,6 @@ import (
 
 	"golang.org/x/net/context"
 
-	"github.com/luci/luci-go/common/errors"
 	"github.com/luci/luci-go/common/logging"
 	"github.com/luci/luci-go/common/retry"
 	"golang.org/x/net/context/ctxhttp"
@@ -58,14 +57,13 @@ func (c *client) call(ctx context.Context, method, urlStr string, body interface
 			}
 			res, err := ctxhttp.Do(ctx, c.HTTP, req)
 			if err != nil {
-				return errors.WrapTransient(err)
+				return retry.Tag.Apply(err)
 			}
 
 			defer res.Body.Close()
 			if res.StatusCode >= 500 {
 				bodyBytes, _ := ioutil.ReadAll(res.Body)
-				return errors.WrapTransient(fmt.Errorf(
-					"status %s: %s", res.Status, bodyBytes))
+				return retry.Tag.Apply(fmt.Errorf("status %s: %s", res.Status, bodyBytes))
 			}
 
 			response, err = ioutil.ReadAll(res.Body)