[OC-8662] - extend platform support and testing

* Add Debian 6 box
* Add SLES 11 box, with note in the TESTING.md
* Add OmniOS r151006c box, with note in the TESTING.md
* Add a test for SMF service recipe, which excludes every platform but
  OmniOS
* Add the client_fork option to the config hash by default if it
  exists in Chef::Config
* Test that the client_fork option is rendered in the config file