(FACT-451) Add Cumulus Linux distro to Debian OS family

Cumulus Linux should report Debian for the osfamily fact.

Conflicts:
	lib/facter/osfamily.rb
	spec/unit/osfamily_spec.rb
Merge branch 'pr/658' into stable

* pr/658:
  (FACT-451) Add Cumulus Linux distro to Debian OS family

This closes GH-658.