Butler: export Coordinator host in environment.

logdog/client/butlerlib/bootstrap/environment.go

 // Copyright 2015 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 bootstrap
 
 // Environment variable names
 const (
         // EnvStreamServerPath is the path to the Butler's stream server endpoint.
         //
         // This can be used by applications to initiate a new Butler stream with an
         // existing Butler stream server process. If a subprocess is launched with a
         // stream server configuration, it will propagate this path to its child
         // processes.
         EnvStreamServerPath = "LOGDOG_STREAM_SERVER_PATH"
 
         // EnvStreamProject is the environment variable set to the configured stream
         // project name.
         EnvStreamProject = "LOGDOG_STREAM_PROJECT"
 
         // EnvStreamPrefix is the environment variable set to the configured
         // stream name prefix.
         EnvStreamPrefix = "LOGDOG_STREAM_PREFIX"
+
+        // EnvCoordinatorHost is the environment variable set to the host name of
+        // the upstream Coordinator service.
+        EnvCoordinatorHost = "LOGDOG_COORDINATOR_HOST"
 )