Merge pull request #21635 from yangdongsheng/qos_read_write

librbd: support bps throttle and throttle read and write seperately.

Reviewed-by: Jason Dillaman <dillaman@redhat.com>

diff --cc src/common/Throttle.h
Simple merge

diff --cc src/common/options.cc
Simple merge

diff --cc src/librbd/ImageCtx.cc
Simple merge

diff --cc src/librbd/ImageCtx.h
Simple merge