Account for multiple nodes in cat indices test

The cat indices health status test tests that the response can be
filtered based on the health status of an index. However, this test was
implicitly relying on the fact that there was only one data node. This
commit modifies this test to account for the fact that there could be
multiple data nodes active in the cluster under test.

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

@@ -72,6 +72,12 @@
 
 ---
 "Test cat indices using health status":
+
+  - do:
+      cluster.health: {}
+
+  - set: { number_of_data_nodes: count }
+
   - do:
       indices.create:
         index: foo
@@ -85,7 +91,7 @@
         body:
           settings:
             number_of_shards: "1"
-            number_of_replicas: "1"
+            number_of_replicas: $count
 
   - do:
       cat.indices: