Ensure index is green after closing in test (#47541)

This test was less stable following a backport as the shards in these
indices did not always show up as allocated immediately after closing
them. This ensures those shards have stabilized before trying to roll
over.

Author: gwbrown

server/src/test/java/org/elasticsearch/action/admin/indices/rollover/RolloverIT.java

@@ -423,6 +423,7 @@ public void testRolloverWithClosedWriteIndex() throws Exception {
 
         assertAcked(client().admin().indices().prepareClose(closedIndex).get());
         assertAcked(client().admin().indices().prepareClose(writeIndexPrefix + "000001").get());
+        ensureGreen(aliasName);
 
         RolloverResponse rolloverResponse = client().admin().indices().prepareRolloverIndex(aliasName)
             .addMaxIndexDocsCondition(1)