fwtool: generate rules in primary input/output chain

fwtool: generate rules in primary input/output chain

Using a single chain integrates with Puppet better, allowing it to
manage chains by default and fwtool rules being added to a pair of
explicitly unmanaged chains. If ferm is managing the entire firewall,
there's not much clarity lost over jumping to external user chains.

Adds a comment with the username to input/output rules as
well (missing from input before).