Can't transition from write survey to normal mode

patch by jasobrown; reviewed by driftx for CASSANDRA-9740

CHANGES.txt

@@ -1,4 +1,5 @@
 2.0.17
+ * Can't transition from write survey to normal mode (CASSANDRA-9740)
  * Avoid NPE in AuthSuccess#decode (CASSANDRA-9727)
  * Add listen_address to system.local (CASSANDRA-9603)
  * Bug fixes to resultset metadata construction (CASSANDRA-9636)

src/java/org/apache/cassandra/service/StorageService.java

@@ -907,7 +907,7 @@ public class StorageService extends NotificationBroadcasterSupport implements IE
 
     public boolean isJoined()
     {
-        return joined;
+        return joined && !isSurveyMode;
     }
 
     public void rebuild(String sourceDc)