* Install thrift on traivis
 * PartitionManager::add_index()
 + Added MockKeyValueStore
 + Added gmock to partition manager test
 + Install thrift manually in travis-ci
 + Added KeyValueStore::open()
 + Added PartitionManager::init()
 + Added string_to_partiton_map() to translate the buffer -> protobuf -> PartitionMap
 * Test initialize with an nonexisted db.
 + PartitionManager insert partition into LevelDB in synchronized way
 + Added test case for GetAllPartitions