Exercise multi-part uploads in S3 repo analysis tests (elastic#125669)

Extends the max blob size to 10MiB, and sets the buffer size to 5MiB, to
ensure that sometimes the S3 repo analysis tests will create blobs using
the multipart upload flow.

Author: DaveCTurner

x-pack/plugin/snapshot-repo-test-kit/qa/s3/src/javaRestTest/java/org/elasticsearch/repositories/blobstore/testkit/analyze/S3RepositoryAnalysisRestIT.java

@@ -9,6 +9,7 @@
 import fixture.s3.S3HttpFixture;
 
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.test.cluster.ElasticsearchCluster;
 import org.elasticsearch.test.cluster.local.distribution.DistributionType;
 import org.junit.ClassRule;
@@ -59,6 +60,7 @@ protected Settings repositorySettings() {
             .put("bucket", bucket)
             .put("base_path", basePath)
             .put("delete_objects_max_size", between(1, 1000))
+            .put("buffer_size", ByteSizeValue.ofMb(5)) // so some uploads are multipart ones
             .build();
     }
 }

x-pack/plugin/snapshot-repo-test-kit/src/test/java/org/elasticsearch/repositories/blobstore/testkit/analyze/AbstractRepositoryAnalysisRestTestCase.java

@@ -29,7 +29,7 @@ public void testRepositoryAnalysis() throws Exception {
         final Request request = new Request(HttpPost.METHOD_NAME, "/_snapshot/" + repository + "/_analyze");
         request.addParameter("blob_count", "10");
         request.addParameter("concurrency", "4");
-        request.addParameter("max_blob_size", "1mb");
+        request.addParameter("max_blob_size", randomFrom("1mb", "10mb"));
         request.addParameter("timeout", "120s");
         request.addParameter("seed", Long.toString(randomLong()));
         assertOK(client().performRequest(request));