puppetlabs/firewall : Tries to delete chains which is INTERNAL_CHAINS

When we use the firewall module, on some servers it tries to remove chains that match INTERNAL_CHAINS (INPUT, OUTPUT, etc).

Example output:

Warning: Firewallchain[PREROUTING:nat:IPv4](provider=iptables_chain): Attempting to destroy internal chain PREROUTING:nat:IPv4
Error: Execution of '/sbin/iptables -t nat -X PREROUTING' returned 1: iptables: Invalid argument. Run `dmesg' for more information.
Error: /Stage[main]/Firewallnetmatch/Firewallchain[PREROUTING:nat:IPv4]/ensure: change from present to absent failed: Execution of '/sbin/iptables -t nat -X PREROUTING' returned 1: iptables: Invalid argument. Run `dmesg' for more information.

Relevant Ruby code:

def destroy
  allvalidchains do |t, chain, table|
    if chain =~ INTERNAL_CHAINS
      # can't delete internal chains
      warning "Attempting to destroy internal chain #{@resource[:name]}"
    end
    debug "Deleting chain #{chain} on table #{table}"
    t.call ['-t', table, '-X', chain]
  end
end

Here it will warn if it encounters one of those chains, but will happily continue trying to delete the chain. Since we should never try deleting an internal chain, IMHO it would be better to just return. (And not warn? But that's up for debate.)