Fix flaky test S3BlobStoreRepositoryTests.testRequestStats

If a BlobStoreRepository is created, but the blobStore() method is never
called, then the actual blobStore instance won't be created. This means
the repository will always emit non-detailed empty stats. When we would
try to merge these stats with another repository that was initialized,
it would fail the assertion that they either both have detailed stats or
neither did.

This fix looks like it's checking if the blobStore has been
initialized, but by calling blobStore(), it's making sure that it gets
initialized.

Signed-off-by: Michael Froh <froh@amazon.com>

plugins/repository-s3/src/internalClusterTest/java/org/opensearch/repositories/s3/S3BlobStoreRepositoryTests.java

@@ -73,7 +73,6 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Objects;
 import java.util.stream.StreamSupport;
 
 import fixture.s3.S3HttpHandler;
@@ -206,7 +205,12 @@ public void testRequestStats() throws Exception {
             } catch (RepositoryMissingException e) {
                 return null;
             }
-        }).filter(Objects::nonNull).map(Repository::stats).reduce(RepositoryStats::merge).get();
+        }).filter(b -> {
+            if (b instanceof BlobStoreRepository) {
+                return ((BlobStoreRepository) b).blobStore() != null;
+            }
+            return false;
+        }).map(Repository::stats).reduce(RepositoryStats::merge).get();
 
         Map<BlobStore.Metric, Map<String, Long>> extendedStats = repositoryStats.extendedStats;
         Map<String, Long> aggregatedStats = new HashMap<>();