Fixes REST test that is designed to timeout on index creation by

making the test wait until all urgent requests are completed before
finishing, so that tear down can properly delete the created index
and cleanup. Without this wait, it was possible that the test would
finish and cleanup the deleted indices would happen before the
index creation even processed, causing the test to leave a created
index behind.

rest-api-spec/src/main/resources/rest-api-spec/test/indices.create/10_basic.yaml

@@ -45,6 +45,10 @@
 
   - match: { shards_acknowledged: false }
 
+  - do:
+      cluster.health:
+          wait_for_events: urgent      
+
 ---
 "Create index with wait_for_active_shards set to all":