enable snapshots

Just an idea:

    irb(main):001:0> partitions = [{"mount" => "/var", "used_fs" => :xfs}, {"mount" => "/", "used_fs" => :btrfs}]
    => [{"mount"=>"/var", "used_fs"=>:xfs}, {"mount"=>"/", "used_fs"=>:btrfs}]
    irb(main):002:0> root_partition = partitions.find{|p| p["mount"] == "/" && p["used_fs"] == :btrfs}
    => {"mount"=>"/", "used_fs"=>:btrfs}
    irb(main):003:0> root_partition["userdata"] = { "/" => "snapshots" } if root_partition
    => {"/"=>"snapshots"}
    irb(main):004:0> partitions
    => [{"mount"=>"/var", "used_fs"=>:xfs}, {"mount"=>"/", "used_fs"=>:btrfs, "userdata"=>{"/"=>"snapshots"}}]