Revert "Enable maintainConnectionCache"

This reverts commit 517fd7741d1a1b56ab710ca3a7a1bdb2e836cc40.

2017-09-08 00:12:07,550 ERROR zuul.Scheduler: Exception in management event:
Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/zuul/scheduler.py", line 783, in process_management_queue
    self._doTenantReconfigureEvent(event)
  File "/usr/local/lib/python3.5/dist-packages/zuul/scheduler.py", line 485, in _doTenantReconfigureEvent
    self._reconfigureTenant(tenant)
  File "/usr/local/lib/python3.5/dist-packages/zuul/scheduler.py", line 588, in _reconfigureTenant
    self.maintainConnectionCache()
  File "/usr/local/lib/python3.5/dist-packages/zuul/scheduler.py", line 731, in maintainConnectionCache
    connection.maintainCache(relevant)
  File "/usr/local/lib/python3.5/dist-packages/zuul/driver/github/githubconnection.py", line 574, in maintainCache
    for key, change in self._change_cache.items():

This causes tenant reconfiguration to abort halfway through which can
cause changes to get stuck in a gate pipeline.

Specifically to reproduce this error, we need two changes in gate, the first
is a config (zuul.yaml) change, and some pull requests in the github cache.

When the first change lands, zuul will perform a reconfiguration and fail.
Then when the second change completes jobs, it will report and claim to be
removed from the queue, but it will still actually be there.

Change-Id: I32e4a4f864ad16be391f57793f1a3abecdd6eee8
diff --git a/zuul/scheduler.py b/zuul/scheduler.py
index 269e049..52b34ec 100644
--- a/zuul/scheduler.py
+++ b/zuul/scheduler.py
@@ -585,7 +585,8 @@
 
             self._reenqueueTenant(old_tenant, tenant)
 
-        self.maintainConnectionCache()
+        # TODOv3(jeblair): update for tenants
+        # self.maintainConnectionCache()
         self.connections.reconfigureDrivers(tenant)
 
         # TODOv3(jeblair): remove postconfig calls?
@@ -718,6 +719,7 @@
                 self.run_handler_lock.release()
 
     def maintainConnectionCache(self):
+        # TODOv3(jeblair): update for tenants
         relevant = set()
         for tenant in self.abide.tenants.values():
             for pipeline in tenant.layout.pipelines.values():
@@ -727,7 +729,7 @@
                 for item in pipeline.getAllItems():
                     relevant.add(item.change)
                     relevant.update(item.change.getRelatedChanges())
-        for connection in self.connections.connections.values():
+        for connection in self.connections.values():
             connection.maintainCache(relevant)
             self.log.debug(
                 "End maintain connection cache for: %s" % connection)