Bug 1147559 - Optimize mulet/b2g-desktop builds by using isolated worker types r=me a=config-only

--HG--
extra : rebase_source : 7d90e64b6c4ac049b118da956bac8fc16bf24bba
extra : source : d4ac71f652f67c600cfc721201731f51137216b0
extra : histedit_source : 702b8cd58e65d805777a7c79a6c758b4b30e335e

testing/taskcluster/tasks/builds/b2g_desktop_debug.yml

@@ -6,7 +6,7 @@ $inherits:
 task:
   scopes:
       - 'docker-worker:cache:workspace-b2g-desktop-objects-debug'
-
+  workerType: b2g-desktop-debug
   extra:
     treeherder:
       collection:

testing/taskcluster/tasks/builds/b2g_desktop_opt.yml

@@ -6,7 +6,7 @@ $inherits:
 task:
   scopes:
       - 'docker-worker:cache:workspace-b2g-desktop-objects-opt'
-
+  workerType: b2g-desktop-opt
   payload:
     cache:
       workspace-b2g-desktop-objects-opt: '/home/worker/workspace'

testing/taskcluster/tasks/builds/mulet_linux.yml

@@ -5,7 +5,7 @@ task:
     name: '[TC] Mulet Linux'
     description: Mulet Linux
 
-  workerType: b2gbuild-desktop
+  workerType: mulet-opt
   scopes:
     - 'docker-worker:cache:build-mulet-linux-workspace'
     - 'docker-worker:cache:tooltool-cache'
@@ -43,4 +43,3 @@ task:
     locations:
       build: 'public/build/target.linux-x86_64.tar.bz2'
       tests: 'public/build/target.tests.zip'
-