Add rados_types.h header file

Signed-off-by: David Zafman <david.zafman@inktank.com>
librados: expose a list of watchers on an object

Add new op CEPH_OSD_OP_LIST_WATCHERS
Add Objecter handling

Signed-off-by: David Zafman <david.zafman@inktank.com>
Add ObjectReadOperation and IoCtx functions

Signed-off-by: David Zafman <david.zafman@inktank.com>
Add listwatchers command to rados

Signed-off-by: David Zafman <david.zafman@inktank.com>
Add test for list_watchers() C++ interface

Signed-off-by: David Zafman <david.zafman@inktank.com>
Merge branch 'wip-3403-4-rebase'

Feature: #3403

Signed-off-by: David Zafman <david.zafman@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>