TEST: Lower num of shards in testShrinkIndexPrimaryTerm

In some cases testShrinkIndexPrimaryTerm creates then 'mutates' 210
shards. If each shard opens more than 10 files (translog, lucene index),
we exceeded the maximum allowed file handles. In our test, the number of
file handles is limited to 2048 by HandleLimitFS. This commit reduces
the number of shards in testShrinkIndexPrimaryTerm to avoid such errors.

Author: dnhatn

server/src/test/java/org/elasticsearch/action/admin/indices/create/ShrinkIndexIT.java

@@ -47,6 +47,7 @@
 import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.collect.ImmutableOpenMap;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.IndexService;
@@ -153,7 +154,7 @@ public void testCreateShrinkIndexToN() {
 
     public void testShrinkIndexPrimaryTerm() throws Exception {
         final List<Integer> factors = Arrays.asList(2, 3, 5, 7);
-        final List<Integer> numberOfShardsFactors = randomSubsetOf(scaledRandomIntBetween(1, factors.size()), factors);
+        final List<Integer> numberOfShardsFactors = randomSubsetOf(scaledRandomIntBetween(1, factors.size() - 1), factors);
         final int numberOfShards = numberOfShardsFactors.stream().reduce(1, (x, y) -> x * y);
         final int numberOfTargetShards = randomSubsetOf(numberOfShardsFactors).stream().reduce(1, (x, y) -> x * y);
         internalCluster().ensureAtLeastNumDataNodes(2);
@@ -164,8 +165,8 @@ public void testShrinkIndexPrimaryTerm() throws Exception {
         assertThat(dataNodes.size(), greaterThanOrEqualTo(2));
         final DiscoveryNode[] discoveryNodes = dataNodes.values().toArray(DiscoveryNode.class);
         final String mergeNode = discoveryNodes[0].getName();
-        ensureGreen();
-
+        // This may need more time than the default value if a large number of shards were created.
+        ensureGreen(TimeValue.timeValueSeconds(120));
         // fail random primary shards to force primary terms to increase
         final Index source = resolveIndex("source");
         final int iterations = scaledRandomIntBetween(0, 16);