Fix 'Too many open files' error in JoinFuzzer (facebookincubator#8702)

Summary:
Pull Request resolved: facebookincubator#8702

By default, Hive Connector caches 20'000 file handles. This leads to "Too many
open files" errors on some systems. Limit the number of cached file handles to
1'000.

Reviewed By: Yuhta

Differential Revision: D53535323

fbshipit-source-id: 2a995bd596aa28c2f8182ed5a8a640ba9806cabb

velox/exec/tests/JoinFuzzer.cpp

@@ -140,11 +140,15 @@ class JoinFuzzer {
 JoinFuzzer::JoinFuzzer(size_t initialSeed)
     : vectorFuzzer_{getFuzzerOptions(), pool_.get()} {
   filesystems::registerLocalFileSystem();
+
+  // Make sure not to run out of open file descriptors.
+  const std::unordered_map<std::string, std::string> hiveConfig = {
+      {connector::hive::HiveConfig::kNumCacheFileHandles, "1000"}};
   auto hiveConnector =
       connector::getConnectorFactory(
           connector::hive::HiveConnectorFactory::kHiveConnectorName)
-          ->newConnector(kHiveConnectorId, std::make_shared<core::MemConfig>());
-  connector::registerConnector(hiveConnector);
+          ->newConnector(
+              kHiveConnectorId, std::make_shared<core::MemConfig>(hiveConfig));
 
   seed(initialSeed);
 }