Build only 2 changes at a time

The GCE nodes are not online anymore and with the current
slaves we have, it is better to reduce the parallelism to
avoid too much WIP and overload our nodes.

Change-Id: Ib4d6474e5df25f1c3305ae972483e1c4a704f869
diff --git a/jenkins/gerrit-verifier-flow.groovy b/jenkins/gerrit-verifier-flow.groovy
index 4779d63..20c12b9 100644
--- a/jenkins/gerrit-verifier-flow.groovy
+++ b/jenkins/gerrit-verifier-flow.groovy
@@ -33,7 +33,7 @@
   static int numRetryBuilds = 3
   static int myAccountId = 1022687
   static int waitForResultTimeout = 10000
-  static int maxBuilds = 4
+  static int maxBuilds = 2
   static String verifierJobName = "Gerrit-verifier-change"
 }