The noop-loop does nothing.
The containerd doesn't have any snapshotter buckets at the beginning.
If user uses specific dir as rootfs to create container, and sets
`snapshotter` key to the container, like `overlayfs` by mistake,
the gc scheduler will try to scan the snapshotter and panic.
In order to avoid this case, remove the noop-loop here.
Signed-off-by: Wei Fu <fuweid89@gmail.com>
34672d483d