(#10162) Various fixes for firewallchain resource

(#10162) Various fixes for firewallchain resource

* Convert commands to optional_commands to avoid iptables installation chicken
  & egg scenarios.
* Downcase tables to match the table names in xtables
* Force fully qualifying the name as <table>:<chain>:<protocol>, we can add
  meaningful defaults later.
* puppet resource <name> command wasn't working as expected, but stripping out
  some of the meaningful defaults I was able to get this to work.
* Reformat some of the code to avoid overrunning 80 chars where possible
* Remove trailing whitespace
* Add flush to provider so that resource modifications immediately update the
  resource in reports and when using puppet resource.
* Removed any commented out code
* Improved documentation
* Change policy so its undefined when not set, instead of being :empty
* Fix test mocking so they will run on a Mac