Replace explicit indices with API conventions in yaml tests

Author: eyalkoren

modules/data-streams/src/yamlRestTest/resources/rest-api-spec/test/data_stream/260_logs_failure_store.yml

@@ -34,7 +34,6 @@ teardown:
         name: logs-app-default
   - match: { data_streams.0.name: logs-app-default }
   - length: { data_streams.0.indices: 1 }
-  - set: { data_streams.0.indices.0.index_name: idx0name }
   - match: { data_streams.0.failure_store.enabled: true }
   - length: { data_streams.0.failure_store.indices: 0 }
 
@@ -58,11 +57,10 @@ teardown:
       indices.get_data_stream:
         name: logs-app-default
   - length: { data_streams.0.failure_store.indices: 1 }
-  - set: { data_streams.0.failure_store.indices.0.index_name: fs0name }
 
   - do:
       search:
-        index: $idx0name
+        index: logs-app-default::data
         body:
           query:
             match_all: {}
@@ -72,7 +70,7 @@ teardown:
 
   - do:
       search:
-        index: $fs0name
+        index: logs-app-default::failures
         body:
           query:
             match_all: {}