Call daemon.Mount will increase the refcount of mounted path,
for those previous running containers, `Mount` call will make
the refcount to 2. see
https://github.com/docker/docker/blob/v1.13.0-rc4/daemon/graphdriver/counter.go#L38
```
if !m.check {
m.check = true
if c.checker.IsMounted(path) {
m.count++
}
}
m.count++
```
graphdrive could restore on reboot after #22541, call
daemon.Mount to resore the graphdriver is not necessary.
And call `daemon.Mount` on restorting will mount all the containers
mounted layer even if it was stop.
This fix call Mount and then Unmount to get `BaseFs`
Signed-off-by: Lei Jitang <leijitang@huawei.com>