Use GCP standard instances for alignment tasks (#907)

* Use GCP standard instances for alignment tasks

* Clarify comment

taskcluster/configs/config.prod.yml

@@ -259,3 +259,8 @@ taskcluster:
   #   default: gcp-spot
   worker-classes:
     default: gcp-spot
+    # long-running tasks that don't support restarts with continuation like training tasks
+    alignments-original: gcp-standard
+    alignments-backtranslated: gcp-standard
+    alignments-student: gcp-standard
+    shortlist: gcp-standard