Merge pull request #32497 from zhengchengyao/snap_exists

rbd: add snap_exists method API

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

diff --cc src/include/rbd/librbd.h
Simple merge

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

diff --cc src/pybind/rbd/rbd.pyx
Simple merge

diff --cc src/test/pybind/test_rbd.py
Simple merge