leveldb: testing: Wait for compaction on TestDb_SparseMerge
leveldb: testing: Wait for compaction on TestDb_SparseMerge

trigrass2/goleveldb,btcsuite/goleveldb,rentongzhang/goleveldb,ngaut/goleveldb,syndtr/goleveldb,no2key/goleveldb,zzl0/goleveldb,FactomProject/goleveldb,chai2010/goleveldb,conseweb/goleveldb,hustbill/goleveldb