Fixed DBCompactionTest.SkipStatsUpdateTest
Fixed DBCompactionTest.SkipStatsUpdateTest

Summary:
DBCompactionTest.SkipStatsUpdateTest relies on the number
of files opened during the DB::Open process, but the persisting
options file support altered this number and thus makes
DBCompactionTest.SkipStatsUpdateTest in certain environment.

This patch fixed this test failure.

Test Plan: db_compaction_test

Reviewers: igor, sdong, anthony, IslamAbdelRahman

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D50637

norton/rocksdb,SunguckLee/RocksDB,jalexanderqed/rocksdb,ryneli/rocksdb,facebook/rocksdb,facebook/rocksdb,jalexanderqed/rocksdb,OverlordQ/rocksdb,bbiao/rocksdb,tsheasha/rocksdb,ryneli/rocksdb,Vaisman/rocksdb,Andymic/rocksdb,hobinyoon/rocksdb,OverlordQ/rocksdb,flabby/rocksdb,wat-ze-hex/rocksdb,bbiao/rocksdb,hobinyoon/rocksdb,jalexanderqed/rocksdb,vmx/rocksdb,Andymic/rocksdb,ryneli/rocksdb,hobinyoon/rocksdb,SunguckLee/RocksDB,ryneli/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,wat-ze-hex/rocksdb,norton/rocksdb,wenduo/rocksdb,jalexanderqed/rocksdb,Andymic/rocksdb,vmx/rocksdb,norton/rocksdb,Andymic/rocksdb,jalexanderqed/rocksdb,vmx/rocksdb,wenduo/rocksdb,SunguckLee/RocksDB,flabby/rocksdb,hobinyoon/rocksdb,flabby/rocksdb,wenduo/rocksdb,ryneli/rocksdb,Vaisman/rocksdb,bbiao/rocksdb,OverlordQ/rocksdb,ryneli/rocksdb,Vaisman/rocksdb,vmx/rocksdb,facebook/rocksdb,norton/rocksdb,wat-ze-hex/rocksdb,vmx/rocksdb,wenduo/rocksdb,Andymic/rocksdb,facebook/rocksdb,jalexanderqed/rocksdb,tsheasha/rocksdb,facebook/rocksdb,tsheasha/rocksdb,SunguckLee/RocksDB,facebook/rocksdb,hobinyoon/rocksdb,OverlordQ/rocksdb,norton/rocksdb,bbiao/rocksdb,bbiao/rocksdb,Vaisman/rocksdb,bbiao/rocksdb,ryneli/rocksdb,wenduo/rocksdb,Vaisman/rocksdb,flabby/rocksdb,wat-ze-hex/rocksdb,flabby/rocksdb,wat-ze-hex/rocksdb,OverlordQ/rocksdb,vmx/rocksdb,vmx/rocksdb,tsheasha/rocksdb,bbiao/rocksdb,norton/rocksdb,Andymic/rocksdb,norton/rocksdb,jalexanderqed/rocksdb,tsheasha/rocksdb,wenduo/rocksdb,tsheasha/rocksdb,Vaisman/rocksdb,wat-ze-hex/rocksdb,hobinyoon/rocksdb,hobinyoon/rocksdb,tsheasha/rocksdb,tsheasha/rocksdb,wat-ze-hex/rocksdb,bbiao/rocksdb,facebook/rocksdb,hobinyoon/rocksdb,flabby/rocksdb,Vaisman/rocksdb,SunguckLee/RocksDB,OverlordQ/rocksdb,SunguckLee/RocksDB,wenduo/rocksdb,wenduo/rocksdb,OverlordQ/rocksdb,norton/rocksdb,vmx/rocksdb,facebook/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,flabby/rocksdb,SunguckLee/RocksDB