counter: check for external umounts
counter: check for external umounts

if a previously mounted container was unmounted
externally (e.g. through conmon cleanup for Podman containers), the
ref counter will lose track of it and report it as still mounted.

Closes: https://github.com/containers/storage/issues/697

Signed-off-by: Giuseppe Scrivano <20002b7b24c75512093a71a58285826d5c504fca@redhat.com>

rhatdan/storage,containers/storage,rhatdan/storage,containers/storage,containers/storage,rhatdan/storage