bug 1419778: don't enforce tier verification if either side of dependency is a buildbot bridge task. r=dustin

taskcluster/taskgraph/util/verify.py

@@ -143,8 +143,14 @@ def verify_dependency_tiers(task, taskgraph, scratch_pad):
             return tier
 
         for task in taskgraph.tasks.itervalues():
+            # Buildbot bridge tasks cannot have tiers, so we cannot enforce
+            # this check for them
+            if task.task["workerType"] == "buildbot-bridge":
+                continue
             tier = tiers[task.label]
             for d in task.dependencies.itervalues():
+                if taskgraph[d].task["workerType"] == "buildbot-bridge":
+                    continue
                 if tier < tiers[d]:
                     raise Exception(
                         '{} (tier {}) cannot depend on {} (tier {})'