[errors] Greatly simplify common/errors package.

dm/appengine/deps/util.go

 // Copyright 2017 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package deps
 
 import (
         "github.com/luci/luci-go/common/errors"
         "github.com/luci/luci-go/grpc/grpcutil"
         "google.golang.org/grpc/codes"
 )
 
-func grpcAnnotate(err error, code codes.Code) *errors.Annotator {
-        return errors.Annotate(err).Tag(grpcutil.Tag.With(code))
+func grpcAnnotate(err error, code codes.Code, reason string, args ...interface{}) *errors.Annotator {
+        return errors.Annotate(err, reason, args...).Tag(grpcutil.Tag.With(code))
 }