Tasckluster: add a second macOS worker

Tweak the Salt definition of /Library/LaunchAgents/net.generic.worker.plist
so that the `user` parameter for the template file is not taken
as a parameter for `file.managed`.
(The first run created a file owned by `worker` instead of `root`.)

etc/taskcluster/macos/config/roster

@@ -1,2 +1,4 @@
 mac1:
     host: servo-tc-mac1.servo.org
+mac2:
+    host: servo-tc-mac2.servo.org

etc/taskcluster/macos/states/generic-worker.plist.jinja

@@ -7,7 +7,7 @@
     <key>StandardOutPath</key>   <string>stdout.log</string>
     <key>StandardErrorPath</key> <string>stderr.log</string>
     <key>WorkingDirectory</key>  <string>{{ home }}</string>
-    <key>UserName</key>          <string>{{ user }}</string>
+    <key>UserName</key>          <string>{{ username }}</string>
     <key>ProgramArguments</key>  <array>
         <string>{{ bin }}/generic-worker</string>
         <string>run</string>

etc/taskcluster/macos/states/generic-worker.sls

@@ -46,7 +46,7 @@ GMT:
         provisionerId: proj-servo
         workerType: macos
         workerGroup: servo-macos
-        workerId: mac1
+        workerId: {{ grains["id"] }}
         tasksDir: {{ home }}/tasks
         publicIP: {{ salt.network.ip_addrs()[0] }}
         signingKeyLocation: {{ home }}/key
@@ -85,7 +85,7 @@ GMT:
       bin: {{ bin }}
       etc: {{ etc }}
       home: {{ home }}
-      user: {{ user }}
+      username: {{ user }}
 
 net.generic.worker:
   service.running: