Fix db_universal_compaction_test

Summary:
db_universal_compaction_test is still failing because of
UniversalCompactionNumLevels/DBTestUniversalCompaction.UniversalCompactionSecondPathRatio/0

https://travis-ci.org/facebook/rocksdb/jobs/94949919

Use same approach to fix other tests to fix this test

Test Plan: Run ./db_universal_compaction_test on mac and make sure all the tests pass

Reviewers: kradhakrishnan, yhchiang, rven, anthony, sdong

Reviewed By: sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D51591

db/db_universal_compaction_test.cc

@@ -1095,6 +1095,8 @@ TEST_P(DBTestUniversalCompaction, UniversalCompactionSecondPathRatio) {
   options.arena_block_size = 4 << 10;
   options.level0_file_num_compaction_trigger = 2;
   options.num_levels = 1;
+  options.memtable_factory.reset(
+      new SpecialSkipListFactory(KNumKeysByGenerateNewFile - 1));
   options = CurrentOptions(options);
 
   std::vector<std::string> filenames;