Include appId in __meteor_runtime_config__ for deployed apps

This adds `appId` to the `config.json` generated by the bundler, and uses that
in `boot.js` to initialize `process.env.APP_ID`. This is used by `autoupdate_server.js`
to set `__meteor_runtime_config__`.

tools/isobuild/bundler.js

@@ -1731,11 +1731,13 @@ class ServerTarget extends JsImageTarget {
   // options specific to this subclass:
   // - clientTarget: the ClientTarget to serve up over HTTP as our client
   // - releaseName: the Meteor release name (for retrieval at runtime)
+  // - appIdentifier: the app identifier (for retrieval at runtime)
   constructor (options, ...args) {
     super(options, ...args);
 
     this.clientTargets = options.clientTargets;
     this.releaseName = options.releaseName;
+    this.appIdentifier = options.appIdentifier;
 
     if (! archinfo.matches(this.arch, "os")) {
       throw new Error("ServerTarget targeting something that isn't a server?");
@@ -1774,6 +1776,7 @@ class ServerTarget extends JsImageTarget {
     // server driver alongside the JsImage
     builder.writeJson("config.json", {
       meteorRelease: self.releaseName || undefined,
+      appId: self.appIdentifier || undefined,
       clientPaths: clientTargetPaths
     });
 
@@ -2151,6 +2154,8 @@ exports.bundle = function ({
   var builtBy = "Meteor" + (release.current.name ?
                             " " + release.current.name : "");
 
+  var appIdentifier = projectContext.appIdentifier;
+
   var success = false;
   var serverWatchSet = new watch.WatchSet();
   var clientWatchSet = new watch.WatchSet();
@@ -2204,6 +2209,7 @@ exports.bundle = function ({
         isopackCache: projectContext.isopackCache,
         arch: serverArch,
         releaseName: releaseName,
+        appIdentifier: appIdentifier,
         buildMode: buildOptions.buildMode,
         providePackageJSONForUnavailableBinaryDeps
       };

tools/static-assets/server/boot.js

@@ -31,6 +31,9 @@ __meteor_bootstrap__ = {
   configJson: configJson };
 __meteor_runtime_config__ = { meteorRelease: configJson.meteorRelease };
 
+if (!process.env.APP_ID) {
+  process.env.APP_ID = configJson.appId;
+}
 
 // connect (and some other NPM modules) use $NODE_ENV to make some decisions;
 // eg, if $NODE_ENV is not production, they send stack traces on error. connect