Merge pull request #14079 from liupan1111/wip-support-signal-handler

rbd-nbd: support signal handle for SIGHUP, SIGINT and SIGTERM.

Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn>
Reviewed-by: Jason Dillaman <dillaman@redhat.com>
Reviewed-by: Mykola Golub <mgolub@mirantis.com>

diff --cc src/tools/rbd_nbd/rbd-nbd.cc
Simple merge