Turn off autoReindexIfStale by default

Although the race condition described in I04ac36ea5 is real, in a Lucene
environment it is largely theoretical and hasn't been the cause of
actual bugreports. At any rate, it's always been an issue with the
change index, and is not a regression in 2.15. Disable the check for
now, to give us time to investigate without blocking a new release.

Bug: Issue 8582
Change-Id: Ia0478b5541ac0442d2aa53e33c2dae09bf0c262d
(cherry picked from commit b7da0764e9)

Documentation/config-gerrit.txt

@@ -2726,7 +2726,7 @@ immediately after indexing it. If false, there is a race condition during two
 simultaneous writes that may cause one of the writes to not be reflected in the
 index. The check to avoid this does consume some resources.
 +
-Defaults to true.
+Defaults to false.
 
 ==== Lucene configuration
 

gerrit-server/src/main/java/com/google/gerrit/server/index/change/ChangeIndexer.java

@@ -166,7 +166,7 @@ public class ChangeIndexer {
   }
 
   private static boolean autoReindexIfStale(Config cfg) {
-    return cfg.getBoolean("index", null, "autoReindexIfStale", true);
+    return cfg.getBoolean("index", null, "autoReindexIfStale", false);
   }
 
   /**