Merge pull request #3292 from kylinstorage/rbd-merge-diff-v2

rbd: merge diff files

Reviewed-by: Josh Durgin <jdurgin@redhat.com>
Reviewed-by: Sage Weil <sage@redhat.com>

diff --cc doc/man/8/rbd.rst
Simple merge

diff --cc src/rbd.cc
Simple merge

diff --cc src/test/cli/rbd/help.t
Simple merge