Unmount if fuse program is no longer active
Unmount if fuse program is no longer active

(cherry picked from commit 38ea480e8d3fcf31f07f6ef563b297914a65d45e)

uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend