ceph: implement readv/preadv for sync operation
ceph: implement readv/preadv for sync operation

For readv/preadv sync-operatoin, ceph only do the first iov.
Now implement this.

Signed-off-by: Jianpeng Ma <c2efc80ba27cf31d4676f82b7232757b76911f7a@gmail.com>
Reviewed-by: Yan, Zheng <45e2ee8c8b09e76a9d512320d4eb53c0cd9925c0@intel.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs