tests: unittest_rocksdb_option: do not leak RocksDBStore

before this change, we allocate an instance of `RocksDBStore` with
`new`, but we never free it. and LeanSanitizer points this out:

```
Direct leak of 952 byte(s) in 1 object(s) allocated from:
    #0 0x55f31440bc2d in operator new(unsigned long) (/home/jenkins-build/build/workspace/ceph-pull-requests/build/bin/unittest_rocksdb_option+0xaebc2d) (BuildId: 81b849dbc41cbc6b05d5e603d9ba8a002dab2d24)
    #1 0x55f3144132fd in RocksDBOption_simple_Test::TestBody() /home/jenkins-build/build/workspace/ceph-pull-requests/src/test/objectstore/TestRocksdbOptionParse.cc:17:22
    #2 0x55f3144ecf26 in void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) /home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/src/gtest.cc:2605:10
    #3 0x55f3144a4312 in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) /home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/src/gtest.cc:2641:14
    #4 0x55f314453ccc in testing::Test::Run() /home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/src/gtest.cc:2680:5
    #5 0x55f314455d02 in testing::TestInfo::Run() /home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/src/gtest.cc:2858:11
    #6 0x55f31445733b in testing::TestSuite::Run() /home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/src/gtest.cc:3012:28
    #7 0x55f3144747c8 in testing::internal::UnitTestImpl::RunAllTests() /home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/src/gtest.cc:5723:44
    #8 0x55f3144f5576 in bool testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) /home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/src/gtest.cc:2605:10
    #9 0x55f3144ab1a2 in bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) /home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/src/gtest.cc:2641:14
    #10 0x55f314473b52 in testing::UnitTest::Run() /home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/src/gtest.cc:5306:10
    #11 0x55f31440f690 in RUN_ALL_TESTS() /home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/include/gtest/gtest.h:2486:46
    #12 0x55f31440e4c3 in main /home/jenkins-build/build/workspace/ceph-pull-requests/src/test/unit.cc:45:10
    #13 0x7f0d32551d8f in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
```

in this change, we manage the life cycle of `RocksDBStore` using
a smart pointer. this should address the leak.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>

src/test/objectstore/TestRocksdbOptionParse.cc

@@ -14,7 +14,7 @@ TEST(RocksDBOption, simple) {
   rocksdb::Options options;
   rocksdb::Status status;
   map<string,string> kvoptions;
-  RocksDBStore *db = new RocksDBStore(g_ceph_context, dir, kvoptions, NULL);
+  auto db = std::make_unique<RocksDBStore>(g_ceph_context, dir, kvoptions, nullptr);
   string options_string = ""
 			  "write_buffer_size=536870912;"
 			  "create_if_missing=true;"
@@ -48,7 +48,7 @@ TEST(RocksDBOption, interpret) {
   rocksdb::Options options;
   rocksdb::Status status;
   map<string,string> kvoptions;
-  RocksDBStore *db = new RocksDBStore(g_ceph_context, dir, kvoptions, NULL);
+  auto db = std::make_unique<RocksDBStore>(g_ceph_context, dir, kvoptions, nullptr);
   string options_string = "compact_on_mount = true; compaction_threads=10;flusher_threads=5;";
 
   int r = db->ParseOptionsFromString(options_string, options);