swarming: Add server-side implementation for supplemental bot_config

appengine/swarming/proto/bots.proto

 // Copyright 2016 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.
 
 syntax = "proto2";
 
 
 // Schema for bots.cfg service config file in luci-config.
 //
 // It defines a function bot_id => (required credentials, trusted_dimensions),
@@ skipping 98 matching lines @@
   // If missing or empty, bot connections are rejected.
   optional BotAuth auth = 20;
 
   // Emails of owners of these bots. Optional.
   repeated string owners = 21;
 
   // List of dimensions to assign to these bots.
   //
   // Each dimension is a "<key>:<value>" pair.
   repeated string dimensions = 22;
+
+  // Additional config script to inject into the swarming bot upon handshake.
+  optional string bot_config_script = 23;

[Vadim Sh., 2017/02/14 22:51:16]

can you extract *.proto change (and perhaps validator) into a separate CL to fix
https://bugs.chromium.org/p/chromium/issues/detail?id=558655#c34?

It will also help in case we need to revert this CL.

[M-A Ruel, 2017/02/15 00:36:32]

This was done in 80856c2cca3fb44796a66ed5bc50e3d16168033b. Rebased.

 }
 
 
 // Defines what kind of authentication to perform when handling requests from
 // bots belonging to some bot group.
 message BotAuth {
   // If true, the bot should provide valid X-Luci-Machine-Token header.
   //
   // The machine FQDN embedded in the token should have hostname equal to the
   // bot_id.
@@ skipping 18 matching lines @@
   // valid X-Luci-Machine-Token and whitelisted IP are needed to successfully
   // authenticate.
   //
   // Can also be used on its own (when both require_luci_machine_token and
   // require_service_account are false). In that case IP whitelist is the
   // primary authentication mechanism. Note that in this case all bots that
   // share the IP whitelist are effectively in a single trust domain (any bots
   // can pretend to be some other bot).
   optional string ip_whitelist = 3;
 }