Merge pull request #4983 from yuyuyu101/wip-setallochint-option

librbd: Add option to allow disabling issuing alloc hint

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

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

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

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

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