Merge pull request #7484 from dillaman/wip-14610-infernalis

librbd: flattening an rbd image with active IO can lead to hang

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

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

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

diff --cc src/test/librbd/test_librbd.cc
Simple merge