tools: some modification at RO

tools: some modification at RO

1) : add new data member to ObjectCacheRequest,
     including m_pool_namepace, m_pool_id, m_snap_id,
     m_cache_path
2) : add some log at CacheSession
3) : change pool name to pool_nspace + poo_id + snap_id
4) : change cache file name
5) : add generate_cache_file_name method
6) : modify UT interface

Signed-off-by: Dehao Shang <dehao.shang@intel.com>