Fix unmount issues in the daemon crash and restart lifecycle, w.r.t
graph drivers. This change sets a live container RWLayer's activity
count to 1, so that the RWLayer is aware of the mount. Note that
containerd has experimental support for restore live containers.
Added/updated corresponding tests.
Signed-off-by: Anusha Ragunathan <anusha@docker.com>
(cherry picked from commit 511a70583f)
