Fix comment for REINITIALIZED unassigned reason.

Author: amosbird

server/src/main/java/org/elasticsearch/cluster/routing/UnassignedInfo.java

@@ -139,7 +139,7 @@ public enum Reason {
          */
         REROUTE_CANCELLED,
         /**
-         * When a shard moves from started back to initializing.
+         * Unassigned as a result of the recovery source (the primary shard) changed during initialization.
          */
         REINITIALIZED,
         /**