Merge pull request #8826 from liewegas/wip-bluestore-bitmap-freelist

os/bluestore: bitmap-based freelist using merge operator

Reviewed-by: Allen Samuels <allen.samuels@sandisk.com>
Reviewed-by: xie xingguo <xie.xingguo@zte.com.cn>

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

diff --cc src/os/bluestore/BlueStore.cc
Simple merge

diff --cc src/os/bluestore/BlueStore.h
Simple merge