Support zstd compression.
Support zstd compression.

Signed-off-by: Like Ma <b0889afe495f01c98aa1d3ec1c3c0cd3e5040e27@gmail.com>

stgraber/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,atxwebs/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,atxwebs/lxd,stgraber/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,atxwebs/lxd,stgraber/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd