rados: Fix cache_flush, cache_try_flush, cache_evict and add hit_set_list

Signed-off-by: David Zafman <david.zafman@inktank.com>
Merge pull request #41 from ceph/wip-rados-op-fixes

rados: Fix cache_flush, cache_try_flush, cache_evict and add hit_set_lis...