SERVER-21996 Wait for replication to all nodes before shutting down config server primary in test

(cherry picked from commit ae83937)

Author: stbrody

jstests/sharding/replset_config/autodiscover_config_rs_from_secondary.js

@@ -25,6 +25,10 @@ var seedList = rst.name + "/" + rst.nodes[1].host; // node 1 is guaranteed to no
     MongoRunner.stopMongos(mongos);
 }
 
+// Wait for replication to all config server replica set members to ensure that mongos
+// doesn't read from a stale config server when trying to verify if the initial cluster metadata
+// has been properly written.
+rst.awaitReplication();
 // Now take down the one electable node
 rst.stop(0);
 rst.awaitNoPrimary();