Let TestEnv and FaultInjectEnv use Env of choice (#5886)

Summary:
Instead of hard coding Env::Default in TestEnv and a few other places, use the
DBTestBase::env_ that has been deduced from the constructor.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5886

Test Plan:
```
make check
```

Differential Revision: D17773029

Pulled By: riversand963

fbshipit-source-id: 7ce4e5175a487e9d281ea2c3aae3c41bffd44629

db/db_basic_test.cc

@@ -913,26 +913,26 @@ TEST_F(DBBasicTest, MmapAndBufferOptions) {
 
 class TestEnv : public EnvWrapper {
   public:
-    explicit TestEnv() : EnvWrapper(Env::Default()),
-                close_count(0) { }
+   explicit TestEnv(Env* base_env) : EnvWrapper(base_env), close_count(0) {}
 
    class TestLogger : public Logger {
     public:
      using Logger::Logv;
-        TestLogger(TestEnv *env_ptr) : Logger() { env = env_ptr; }
+     explicit TestLogger(TestEnv* env_ptr) : Logger() { env = env_ptr; }
      ~TestLogger() override {
        if (!closed_) {
          CloseHelper();
        }
      }
-        void Logv(const char* /*format*/, va_list /*ap*/) override{};
+     void Logv(const char* /*format*/, va_list /*ap*/) override {}
 
     protected:
      Status CloseImpl() override { return CloseHelper(); }
 
     private:
      Status CloseHelper() {
-          env->CloseCountInc();;
+       env->CloseCountInc();
+       ;
        return Status::IOError();
      }
      TestEnv* env;
@@ -958,7 +958,8 @@ TEST_F(DBBasicTest, DBClose) {
   ASSERT_OK(DestroyDB(dbname, options));
 
   DB* db = nullptr;
-  TestEnv* env = new TestEnv();
+  TestEnv* env = new TestEnv(env_);
+  std::unique_ptr<TestEnv> local_env_guard(env);
   options.create_if_missing = true;
   options.env = env;
   Status s = DB::Open(options, dbname, &db);
@@ -992,13 +993,11 @@ TEST_F(DBBasicTest, DBClose) {
   ASSERT_EQ(env->GetCloseCount(), 2);
   options.info_log.reset();
   ASSERT_EQ(env->GetCloseCount(), 3);
-
-  delete options.env;
 }
 
 TEST_F(DBBasicTest, DBCloseFlushError) {
   std::unique_ptr<FaultInjectionTestEnv> fault_injection_env(
-      new FaultInjectionTestEnv(Env::Default()));
+      new FaultInjectionTestEnv(env_));
   Options options = GetDefaultOptions();
   options.create_if_missing = true;
   options.manual_wal_flush = true;