lxd/storage/drivers/generic/vfs: Pass --numeric-owner to tar unpack command
lxd/storage/drivers/generic/vfs: Pass --numeric-owner to tar unpack command

This ensures that owner/group name info inside the tarball isn't used to resolve to a different
UID/GID as they are unpacked on the host, and instead ensures they remain the same UID/GID that
they were inside the instance when it was exported.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

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