Fix snapshot ctr command to use default
Fix snapshot ctr command to use default

After the rework of server-side defaults, the `ctr snapshot` command
stopped working due to no default snapshotter.

Signed-off-by: Phil Estes <dbac1f450dc8326caa7ba104b384a0eca642250c@linux.vnet.ibm.com>

estesp/containerd,miaoyq/containerd,mikebrow/containerd,kunalkushwaha/containerd,kunalkushwaha/containerd,containerd/containerd,dmcgowan/containerd,estesp/containerd,dmcgowan/containerd,crosbymichael/containerd,vdemeester/containerd,AkihiroSuda/containerd,containerd/containerd,crosbymichael/containerd,vdemeester/containerd,thaJeztah/containerd,miaoyq/containerd,thaJeztah/containerd,mikebrow/containerd