Increase replication timeout to 5 minutes

For very large projects, when Gerrit is under load, it can take
longer than 60 seconds for the submit action to be processed and the
associated commit to replicate to its local mirror, causing Zuul to
think the change did not merge and resetting any remaining changes
in that dependent queue. Increase this to 5 minutes, since the
impact from these "phantom gate resets" is more significant than any
potential increase in merge wait time.

Change-Id: If57d5ed2720707c1ec3a3477dd229f042789fa1f
diff --git a/zuul/trigger/gerrit.py b/zuul/trigger/gerrit.py
index fe9a1aa..48bf0dd 100644
--- a/zuul/trigger/gerrit.py
+++ b/zuul/trigger/gerrit.py
@@ -107,7 +107,7 @@
 class Gerrit(object):
     name = 'gerrit'
     log = logging.getLogger("zuul.Gerrit")
-    replication_timeout = 60
+    replication_timeout = 300
     replication_retry_interval = 5
 
     def __init__(self, config, sched):