librados.h: Add read/write op fadvise flags LIBRADOS_OP_FLAG_FADVISE_*.

Add four fadvise op flags: RANDOM/SEQUENTIAL/WILLNEED/DONTNEED.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
librados: Add read/write fadvise op flags in ObjectOperationFlags.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
librados: Add read/write fadvise op flags CEPH_OSD_OP_FLAG_FADVISE_*.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
librados: Modify parameter type of librados::ObjectOperation::set_op_flags

After adding four read/write fadvise flags OP_FADVISE_*, those flags
can set different flags at the same time. So change parameter type of
set_op_flags from 'enum ObjectOperationFlags' to int.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
librbd/internal: Modify read/write api to handle op flags.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
librbd: Add m_op_flags in AioRead to track op flags for rbd read.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
librbd: Add set_op_flags in AioWrite to set op_flags for rbd write.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
librbd: add new read/write api for librbd which handle op flags.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>