Add LinuxMint to operating system facts

This commit was cherry-picked from 1938f39.

Conflicts:
	lib/facter/operatingsystemrelease.rb
	lib/facter/osfamily.rb
adding tests for LinuxMint facts

This commit cherry-picks ec6aed48

Conflicts:
	spec/unit/operatingsystemrelease_spec.rb
	spec/unit/osfamily_spec.rb
Merge pull request #695 from Whopper92/port_mint_facts

[FACT-465] Port Linux Mint facts and tests